Rasch Analysis of the Quality of Life and Vision Function Questionnaire

Psychometric Properties under EFA, CFA, Measurement Invariance, and IRT Models for Older Adults' First Aids Knowledge Scale among Iranian Grandparents: The Modified Scale

This research aims to create and evaluate an assessment tool termed Older Adults' First Aid Knowledge Scale, which measures the knowledge and attitude of Iranian grandparents about first aid. In accordance with COSIM guidelines, 485 individuals in southern Iran completed the instrument as part of a psychometric investigation. Rasch partial credit model (PCM), exploratory factor analysis (EFA), confirmatory factor analysis (CFA), and receiver operating characteristic (ROC) analysis were used to analyze the results. The final version of OFAKS consisted of 18 items that were validated through EFA, CFA, and item response theory (IRT) analysis. All items showed measurement invariance and consecutive response groupings in the predictable order, and the instrument had strong internal consistency. Although Rasch's analysis demonstrated the significance of OFAKS, further investigations and testing in different settings are required to confirm the validity of the tool.

Rasch Modelling to Assess Psychometric Validation of the Knowledge about Tuberculosis Questionnaire (KATUB-Q) for the General Population in Indonesia

OBJECTIVE

This study aims to validate and evaluate the psychometric properties of the knowledge about tuberculosis questionnaire (KATUB-Q) for the general population in Indonesia.

METHODS

The KATUB-Q consists of three domains: general knowledge, transmission, and treatment, with 20 dichotomous items. Rasch analysis through WINSTEPS was used.

RESULTS

A total of 504 respondents from 34 provinces in Indonesia completed the survey. Based on the model fit statistics, 3 misfit items were deleted and 17 items were used. Item and person reliability, as well as Cronbach's Alpha values were 0.99, 0.63, and 0.73, respectively, which means they achieved the minimum acceptable limit of 0.6. Based on the results, Indonesia's Person ability analysis indicated a high level of knowledge. KATUB-Q has no significant bias item based on sex found in the differential item functioning analysis.

CONCLUSION

KATUB-Q has 17 items with a valid and reliable instrument; hence, it can be used to measure the knowledge about TB in the general population.

PRACTICE IMPLICATIONS

The unidimensional structure of the core items of the KATUB-Q provides empirical evidence for using the sum score of the items in practice to evaluate the effectiveness of TB education in the general population.

Catquest-9SF questionnaire: Validation in a Greek-speaking population using Rasch analysis

PURPOSE

The Catquest-9SF questionnaire is a tool measuring visual disability and vision-related limitation in patients' daily activities. The primary objective of this study was the validation of Catquest-9SF in a Greek-speaking cataract population.

METHODS

The questionnaire was translated into Greek and translated back into English. A pre-final Greek version was formed and tested by 10 Greek-English bilingual participants and by the translation team, and the final version was produced. Patients scheduled for cataract surgery completed the questionnaire preoperatively and postoperatively. Rasch analysis was performed for the assessment of the Catquest-9SF psychometric properties, including response category ordering, item fit statistics, principal components analysis, precision, differential item functioning and targeting for preoperative and postoperative data collectively.

RESULTS

A total of 100 (55 men, 45 women, mean age = 71.94±6.63) cataract patients completed the Greek version of Catquest-9SF questionnaire preoperatively and postoperatively. Rasch analysis showed a significant improvement in the median person Rasch score from -1.49 preoperatively to -4.71 logits postoperatively, while the effect size was 1.3. Unidimensionality was confirmed since infit and outfit mean square values varied between 0.66 and 1.37. Rasch analysis showed good precision and separation ability (Person Separation Index of 3.28, and Person Reliability of 0.92). Four response categories were found for all items. The item-person means difference was -1.83 logits. The difference between preoperative and postoperative Catquest-9SF logit score was positively correlated with preoperative Catquest-9SF logit score (coeff. = 0.798, p<0.0001) and negatively correlated with postoperative spherical equivalent (coeff. = -0.825, p = 0.011).

CONCLUSION

The Greek version of Catquest-9SF proved to be reliable, valid, unidimensional and responsive to changes after cataract surgery presenting good psychometric properties for cataract patients. Some postoperative mistargeting was found indicating that the tasks were easily performed by respondents after cataract surgery.

TRIAL REGISTRATION

NCT05323526 -retrospectively registered.

[Changes in quality of life of glaucoma patients over a period of 8 years]

PURPOSE

The quality of life (QoL) of glaucoma patients is affected by many factors. In particular, patient activity is compromised by the chronicity of the disease. In this study, we evaluated the change in QoL and its impact on activities over a period of 8 years.

METHODS

A total of 43 patients with glaucomatous optic nerve damage were enrolled in this retrospective longitudinal observational study. Changes in intraocular pressure (IOP), best-corrected visual acuity (BCVA) and visual field (VF) parameters, number of IOP-lowering eye drops and IOP-lowering surgery were assessed over a period of 8 years. Assessment of QoL was obtained by patient-reported visual functioning using the Rasch-calibrated glaucoma activity limitation 9 (GAL-9) questionnaire at baseline and after 8 years.

RESULTS

The BCVA of the better eye changed from 0.16 ± 0.22 to 0.21 ± 0.14 logMAR, whereas there was a change from 0.27 ± 0.25 to 1.39 ± 1.1 logMAR in the worse eye. The VF parameter mean deviation (MD) of the better eye changed from -2.39 ± 4.55 dB to -4.83 ± 5.09 dB, while it altered significantly from -8.86 ± 5.86 dB to -12.05 ± 8.07 dB in the worse eye. Values of GAL‑9 changed from -2.39 ± 2.14 to -1.38 ± 2.78 (in the Rasch analysis, more negative values account for a better QoL), according to a sum score change from 79.17 ± 19.63 to 69.22 ± 27.95. This change showed a highly significant correlation with the MD at follow-up, especially with the worse eye (r = 0.43). The impact of the MD at follow-up on QoL could also be well predicted in a regression model.

CONCLUSION

The QoL of glaucoma patients decreased significantly over time. Changes in the VF, particularly of the worse eye, have a great impact on reported functioning. Careful treatment, especially of the eye with greater glaucomatous damage, is mandatory.

Psychometric Assessment of the Chinese Version of the Indian Vision Functioning Questionnaire Based on the Method of Successive Dichotomizations

Purpose

The purpose of this study was to assess whether a Chinese translated version of the 33-item Indian Vision Function Questionnaire (IND-VFQ-33) forms a valid measurement scale and to evaluate its psychometric properties based on the method of successive dichotomizations (MSD).

Methods

The English version of the IND-VFQ-33 was translated, back translated, and cross-culturally adapted for use in China. It was interviewer administered to patients with cataracts. MSD, a polytomous Rasch model that estimates ordered thresholds, was used to assess and optimize psychometric properties of the overall scale and three subscales separately.

Results

One hundred and seventy-nine patients provided complete responses. After the removal of 2 misfitting items, a revised 31-item overall scale demonstrated adequate precision (person reliability [PR] = 0.92) and no misfitting items. The general functioning subscale fit the MSD model well after removing two misfitting items. The psychosocial impact subscale and the visual symptoms subscale were not considered further due to poor measurement precision. After addressing psychometric deficiencies, a 31-item overall scale (IND-VFQ-31-CN) and a 19-item general functioning subscale (IND-VFQ-GF-19-CN) were developed.

Conclusions

The original IND-VFQ-33 required re-engineering to form valid measures for use in China. The revised overall scale and general functioning subscale demonstrated adequate MSD based psychometric properties.

Translational Relevance

The revised IND-VFQ-33 is a valid patient-reported outcome assessment for Chinese patients with cataract based on MSD analysis.

A very short version of the Visual Function Questionnaire (VFQ-3oo7) for use as a routinely applied Patient-Reported Outcome Measure

BACKGROUND

Patient-reported outcome measures (PROMs) are valuable supplements in regular care to facilitate routine monitoring of quality of life from the patient's perspective. The 25-item National Eye Institute Visual Function Questionnaire (NEI-VFQ-25) is a widely used PROM in ophthalmology. However, the NEI-VFQ-25 is too time-consuming and cumbersome for routine evaluations in regular care. The aim of this study is to construct a 7-item questionnaire of which only 3 items are presented to the patient, by means of routing. This VFQ 3 out of 7 (VFQ-3oo7) should have a minimal loss of information compared with the NEI-VFQ-25.

METHODS

An historical database including 3293 administrations of the NEI-VFQ-25 was constructed involving patients with retinal detachment, cataract, corneal diseases, glaucoma, macular degeneration, uveal melanoma and a normal population sample. The data were subjected to Rasch analyses, in particular a generalized partial credit model. Items were sorted on the latent trait and divided into seven categories. From each category, the item with the highest discriminative value was selected. Through routing, only three out of the seven remaining questions are used, where the answers navigate patients to a fitting trait level.

RESULTS

A one-dimensional structure was considered fitting. The VFQ-3oo7 showed a small loss of information compared with the total score of the NEI-VFQ-25: correlation 0.927 and a relative precision of 0.868.

CONCLUSION

The very short, but valid, VFQ-3oo7 can be applied to evaluate the patient's perceived vision-related health status in routine evaluations of treatments in regular care, with a small burden for patients.

Item response analysis to explore psychometric properties of the Persian version of Troutman successful aging inventory: Rasch partial credit model

The study aimed to evaluate Persian version of the TSAI-2011 to determine successful aging issues in older adults. In a psychometric study, the instrument was completed by 400 men and women aged 60 and above and the Rasch partial credit model was used. The PCM indicated that items 1 and 20 were misfitting. Also, it successive response categories for all items were located in the expected order and version of TSAI with 22-items had more internal consistency. Although Rasch analysis indicated to relevant of TSAI 22-Items, it should be evaluated in further studies and divergent cultures.

Development of Pediatric Eye Questionnaires for Children With Eye Conditions

PURPOSE

To develop patient-derived Pediatric Eye Questionnaires (PedEyeQ) to separately assess eye-related quality of life (ER-QOL) and functional vision in children with eye conditions.

DESIGN

Questionnaire development study.

METHODS

A total of 444 children (0 to <18 years old), across 10 diagnostic categories, were enrolled at 2 sites. All parents (n = 444) and 277 children (5 to <18 years old) completed master questionnaires, developed from patient-derived concerns. Factor analysis was performed to identify unidimensional domains (eigenvalue >1.0) and Rasch analyses (differential item functioning, targeting, fit) to reduce items (separate analyses for subjects aged 0-4, 5-11, and 12-17 years and for each factor).

RESULTS

The Child 5- to 11-year-old PedEyeQ consisted of 4 unidimensional domains/questionnaires: functional vision, bothered by eyes/vision, social, frustration/worry (10 items each). The Child 12- to 17-year-old PedEyeQ consisted of the same 4 domains (total 39 items). The Proxy 0- to 4-year-old PedEyeQ consisted of 3 questionnaires/domains: functional vision, bothered by eyes/vision, social (total 29 items). The Proxy 5- to 11-year-old PedEyeQ consisted of 5 questionnaires/domains: functional vision, bothered by eyes/vision, social, frustration/worry, eye care (total 39 items), as did the Proxy 12- to 17-year-old PedEyeQ (total 42 items). The Parent PedEyeQ consisted of 4 questionnaires/domains: impact on parent/family, worry regarding child's eye condition, worry regarding child's self-perception and interactions, worry regarding child's visual function (total 35 items). Rasch look-up tables were created for scoring.

CONCLUSIONS

By following a rigorous approach, we have developed Pediatric Eye Questionnaires for separately assessing functional vision and ER-QOL domains in children of any age and with any eye condition.

Assessment of Psychometric Properties of an Oral Health Care Measure of Cultural Competence Among Dental Students Using Rasch Partial Credit Model

Reliability, validity, and feasibility of the only validated oral health care measure of cultural competence, the Knowledge, Efficacy, and Practices Instrument (KEPI), have been confirmed. However, the instrument's psychometric properties including item and person reliability, category response functioning, and scale targeting, as well as differential scale functioning for subgroups, have not yet been examined. The aim of this study was to test the psychometric properties of KEPI among dental students using Rasch Partial Credit Model to determine if this model provided broader valid information that cannot be demonstrated according to Classical Test Theory. A total 1,290 dental students in the first or final semester at four U.S. dental schools were invited to participate in the study in 2016. Of those, 1,231 individuals completed the survey, for a 95.4% response rate. The participants were 613 males and 618 females and 889 non-underrepresented minority (URM) and 342 URM students. The Rasch Partial Credit Model assessed the psychometric properties of KEPI's 20 items/three subscales. Differential scale functioning was found in the Culture-Centered Practice and Efficacy of Assessment subscales. Four items were endorsed differentially by gender; four items were endorsed differentially by URM/non-URM students. This study examined the psychometric properties of the KEPI using Rasch analysis to assess differential item functioning by dental student gender and race. The results provided valid evidence for the high internal reliability, measurement properties, and unidimensionality for the KEPI domains, ideal targeting, and well response category functioning, showing that the KEPI is a reliable instrument for measuring the subscales Knowledge of Diversity, Culture-Centered Practice skills, and Efficacy of Assessment for health care providers.

Validation of the Fullerton Advanced Balance Scale in children with cerebral palsy

Background/Aims:

Cerebral palsy is classified by the type of motor impairment. The ability to balance differs depending on the level of disability. The aim of this research was to investigate the item fit and item difficulty of the Fullerton Advanced Balance Scale in children with cerebral palsy, and to compare item fit and difficulty in individuals with diplegia and hemiplegia.

Methods:

Forty children with cerebral palsy completed the 10-item Fullerton Advanced Balance Scale questionnaire. Rasch analysis was used to identify the psychometric properties of the Fullerton Advanced Balance Scale and compare item fit and difficulty in two groups: children with diplegia and children with hemiplegia.

Findings:

Item 2 showed misfit statistics for all participants. Items 1 and 2 showed misfit statistics in hemiplegia, whereas no items showed misfit in diplegia.

Conclusions:

Item fit and difficulty need to be considered in relation to the level of disability when evaluating balance in children with cerebral palsy.

An alternative application of Rasch analysis to assess data from ophthalmic patient-reported outcome instruments

Purpose

To highlight the potential shortcomings associated with the current use Rasch analysis for validation of ophthalmic questionnaires, and to present an alternative application of Rasch analysis to derive insights specific to the cohort of patients under investigation.

Methods

An alternative application of Rasch analysis was used to investigate the quality of vision (QoV) for a cohort of 481 patients. Patients received multifocal intraocular lenses and completed a QoV questionnaire one and twelve months post-operatively. The rating scale variant of the polytomous Rasch model was utilized. The parameters of the model were estimated using the joint maximum likelihood estimation. Analysis was performed on data at both post-operative assessments, and the outcomes were compared.

Results

The distribution of the location of symptoms altered between assessments with the most annoyed patients completely differing. One month post-operatively, the most prevalent symptom was starbursts compared to glare at twelve months. The visual discomfort from the most annoyed patients is substantially higher at twelve months. The current most advocated approach for validating questionnaires using Rasch analysis found that the questionnaire was “Rasch-valid” one month post-operatively and “Rasch-invalid” twelve months post-operatively.

Conclusion

The proposed alternative application of Rasch analysis to questionnaires can be used as an effective decision support tool at population and individual level. At population level, this new approach enables one to investigate the prevalence of symptoms across different cohorts of patients. At individual level, the new approach enables one to identify patients with poor QoV over time. This study highlights some of the potential shortcomings associated with the current use of Rasch analysis to validate questionnaires.

Validating the Quality of Life After Brain Injury Through Rasch Analysis

OBJECTIVE

The Quality of Life after Brain Injury (QOLIBRI), a cross-cultural instrument, has been validated in several languages; however, traditional psychometric approaches have critical limitations. Therefore, we applied the Rasch model for validating the 37-item QOLIBRI scale among a Chinese population with traumatic brain injury.

PARTICIPANTS AND SETTING

In total, 587 participants (mean age: 44.2 ± 15.4 years; women, 46.3%) were surveyed in neurosurgery departments at 6 hospitals in Taipei, Taiwan.

MAIN OUTCOME MEASURE

The QOLIBRI.

RESULTS

Of the 6 subscales of the QOLIBRI, 4 (cognition, self, daily life and autonomy, and social relationships) were unidimensional, valid, and reliable, whereas the remaining 2 (emotions and physical problems) exhibited poor unidimensionality, item and person reliability, and person-item targeting. Five items (energy, concentrating, getting out and about, sex life, and achievements) showed considerable differential item functioning among age groups, disability levels, and time since traumatic brain injury.

CONCLUSION

According to item response theory, we identified psychometric issues in the emotions and physical problems subscales of the QOLIBRI as well as several differential item functioning items. Future research is required to determine whether similar results are observed in other language versions of the QOLIBRI or in other countries.

Development and validation of the canine visual function instrument

OBJECTIVE

In this study, we created the Canine Visual Function Instrument (CVFI) and tested its validity and reliability for assessing the quality of vision of dogs.

METHODS

We used Cronbach's alpha to test the strength of the consistency of the questions in the instrument and factor analysis to assess whether the questions achieved unidimensionality in the measurement of dogs' vision quality.

RESULTS

Our analysis shows that the CVFI is a valid and reliable tool to seek self-reported observations about dogs' vision quality from owners. Our results also show that the vision quality scale has high empirical validity and therefore can be used to determine whether a dog has normal vision or moderate or serious visual impairments.

CONCLUSION

The CVFI might have important practical applications in the field of veterinary ophthalmology in two important ways. First, it can be used to determine whether the treatment of dogs with visual impairment improves vision quality. Second, it can be used as a warning system to alert owners about their dogs' quality of vision.

Catquest-9SF questionnaire: validation of Malay and Chinese-language versions using Rasch analysis

Background

Catquest questionnaire was originally developed in Swedish to measure patients’ self-assessed visual function to evaluate the benefit of cataract surgery. The result of the Rasch analysis leading to the creation of the nine-item short form of Catquest, (Catquest-9SF), and it had been translated and validated in English. The aim is therefore to evaluate the translated Catquest-9SF questionnaire in Malay and Chinese (Mandarin) language version for measuring patient-reported visual function among cataract population in Malaysia.

Methods

The English version of Catquest-9SF questionnaire was translated and back translated into Malay and Chinese languages. The Malay and Chinese translated versions were self-administered by 236 and 202 pre-operative patients drawn from a cataract surgery waiting list, respectively. The translated Catquest-9SF data and its four response options were assessed for fit to the Rasch model.

Results

The Catquest-9SF performed well in the Malay and Chinese translated versions fulfilling all criteria for valid measurement, as demonstrated by Rasch analysis. Both versions of questionnaire had ordered response thresholds, with a good person separation (Malay 2.84; and Chinese 2.59) and patient separation reliability (Malay 0.89; Chinese 0.87). Targeting was 0.30 and −0.11 logits in Malay and Chinese versions respectively, indicating that the item difficulty was well suited to the visual abilities of the patients. All items fit a single overall construct (Malay infit range 0.85–1.26, outfit range 0.73–1.13; Chinese infit range 0.80–1.51, outfit range 0.71–1.36), unidimensional by principal components analysis, and was free of Differential Item Functioning (DIF).

Conclusions

These results support the good overall functioning of the Catquest-9SF in patients with cataract. The translated questionnaire to Malay and Chinese-language versions are reliable and valid in measuring visual disability outcomes in the Malaysian cataract population.

Analysis and comparison of the psychometric properties of two balance scales for elderly adults

Background/Aims:

The aim of this research was to verify psychometric properties of the Berg Balance Scale and the Fullerton Advanced Balance Scale, and compare the item difficulty between the two scales.

Methods:

A total of 97 community-dwelling older adults participated in this study. All participants were assessed on their degree of balance ability by the Berg Balance Scale and the Fullerton Advanced Balance Scale, respectively. We identified the psychometric properties and compared the item difficulty of the two scales using the Rasch analysis.

Findings:

Among the items on the Berg Balance Scale, the Standing to sitting and Transfers items showed misfit statistics. The most difficult item was Standing on one foot, whereas the easiest item was Sitting unsupported. In the case of the Fullerton Advanced Balance Scale, the Standing with feet together and eyes closed, Stand on foam, eyes closed and Walk with head turns items showed misfit statistics. Also, the most difficult item was Stand on one leg (logit value, 2.93), whereas the easiest item was Turn in full circle. Among the 24 items of the combined Berg Balance Scale and Fullerton Advanced Balance Scale, 13 items (nine items for the Fullerton Advanced Balance Scale and four items on the Berg Balance Scale) had positive logit values, and 11 items (one item on the FAB and 10 on the Berg Balance Scale) had negative logit values.

Conclusions:

Both the Berg Balance Scale and the Fullerton Advanced Balance appear to be reliable and valid tools to assess balance function in older adults. However, the Berg Balance Scale is suitable for assessing balance ability in a group of lower functioning older adults, whereas, the Fullerton Advanced Balance is suitable for assessing balance ability in a group of higher functioning older adults.

Initial validation of the dimensions of home measure

BACKGROUND

Research has established a need to consider further aspects of the home environment in home modification provision and evaluation. The Dimensions of Home Measure (DOHM) was developed as a self-report outcome measurement tool for home modification practice to meet this need. Its development was informed by a literature review and qualitative exploration which identified six dimensions of the home environment: the physical, social, personal, temporal, occupational and societal dimensions which contribute to one's experience of home. This paper reports the initial evaluation of the validity of the DOHM.

METHOD

The DOHM was completed by 163 community dwelling older adults and people with disabilities. The Rasch measurement model was used to evaluate three aspects of construct validity: rating scale structure, unidimensionality and targeting.

RESULTS

The five-point DOHM rating scale function was evaluated using Linacre's (2002) guidelines. The middle rating category did not function well, and this resulted in collapsing the rating scale from five to four points. The unidimensionality of the DOHM's subscales was supported by Rasch-based principal component analysis and item fit analysis. However, hierarchical results of item difficulties revealed significant gaps in each of the DOHM's subscales, indicating that more items will be needed to capture the full range of participant's experiences of home.

CONCLUSION

The DOHM was developed to provide a relevant evaluation tool for home modification practice which comprehensively measures the home environment. This study identified preliminary validity of this tool, with revision and further psychometric validation required.

Measuring Health-Related Quality of Life in Strabismus: A Modification of the Adult Strabismus-20 (AS-20) Questionnaire Using Rasch Analysis

Purpose

To evaluate the psychometric properties of the Adult Strabismus-20 (AS-20)- a health-related quality of life (HRQoL) questionnaire in adults with strabismus, and if flawed, to revise the AS-20 and its subscales creating valid measurement scales.

Methods

584 adults (meanage, 27.5 years) with strabismus were recruited from an outpatient clinic at a South Indian tertiary eye care centre and were administered the AS-20 questionnaire.The AS-20 was translated and back translated into two Indian languages. The AS-20 and its two 10-item subscales – ‘psychosocial’ and ‘function’were assessed separately for fit to the Rasch model, including an assessment of the rating scale, unidimensionality (by principal components analysis), measurement precision by person separation reliability, PSR, targeting, and differential item functioning (DIF; notable > 1.0 logits).

Results

Response categories were not used as intended, thereby, required re-organization and reducing their number from 5 to 3. The AS-20 had adequate measurement precision (PSR = 0.87) but lacked unidimensionality; however, deletion of the six multi-dimensionality causing items and an additional three misfitting items resulted in 11-item unidimensional questionnaire (AS-11). Two items failed to satisfy the model expectations in the ‘psychosocial’ subscale and were deleted – resulting in an 8-item unidimensional scale with adequate PSR (0.81) and targeting (0.23 logits). One item misfit in the ‘function’ subscale and was deleted—resulting in a 9 item Rasch-revised unidimensional subscale with acceptable PSR (0.80) and targeting (0.97 logits).None of the items displayed notable DIF by age, gender and level of education.

Conclusions

The AS-11 and its two Rasch-revised subscales – 8-item psychosocial and 9-item function subscale may be more appropriate than the original AS-20 and its two 10-item subscales for use as unidimensional measures of HRQoL in adults with strabismus in India. Further work is required to establish the validity of the revised rating scale.

Measuring coping in parents of children with disabilities: a rasch model approach

Background

Parents of a child with disability must cope with greater demands than those living with a healthy child. Coping refers to a person’s cognitive or behavioral efforts to manage the demands of a stressful situation. The Coping Health Inventory for Parents (CHIP) is a well-recognized measure of coping among parents of chronically ill children and assesses different coping patterns using its three subscales. The purpose of this study was to provide further insights into the psychometric properties of the CHIP subscales in a sample of parents of children with disabilities.

Methods

In this cross-sectional study, 220 parents (mean age, 33.4 years; 85% mothers) caring for a child with disability enrolled in special schools as well as in mainstream schools completed the 45-item CHIP. Rasch analysis was applied to the CHIP data and the psychometric performance of each of the three subscales was tested. Subscale revision was performed in the context of Rasch analysis statistics.

Results

Response categories were not used as intended, necessitating combining categories, thereby reducing the number from 4 to 3. The subscale – ‘maintaining social support’ satisfied all the Rasch model expectations. Four item misfit the Rasch model in the subscale –maintaining family integration’, but their deletion resulted in a 15-item scale with items that fit the Rasch model well. The remaining subscale – ‘understanding the healthcare situation’ lacked adequate measurement precision (<2.0 logits).

Conclusions

The current Rasch analyses add to the evidence of measurement properties of the CHIP and show that the two of its subscales (one original and the other revised) have good psychometric properties and work well to measure coping patterns in parents of children with disabilities. However the third subscale is limited by its inadequate measurement precision and requires more items.

Identifying content for the glaucoma-specific item bank to measure quality-of-life parameters

PURPOSE

Patient-reported outcomes (PROs) have become essential clinical trial end points. However, a comprehensive, multidimensional, patient-relevant, and precise glaucoma-specific PRO instrument is not available. Therefore, the purpose of this study was to identify content for a new, glaucoma-specific, quality-of-life (QOL) item bank.

METHODS

Content identification was undertaken in 5 phases: (1) identification of extant items in glaucoma-specific instruments and the qualitative literature; (2) focus groups and interviews with glaucoma patients; (3) item classification and selection; (4) expert review and revision of items; and (5) cognitive interviews with patients.

RESULTS

A total of 737 unique items (extant items from PRO instruments, 247; qualitative articles, 14 items; focus groups and semistructured interviews, 476 items) were identified. These items were classified into 10 QOL domains. Four criteria (item redundancy, item inconsistent with domain definition, item content too narrow to have wider applicability, and item clarity) were used to remove and refine the items. After the cognitive interviews, the final minimally representative item set had a total of 342 unique items belonging to 10 domains: activity limitation (88), mobility (20), visual symptoms (19), ocular surface symptoms (22), general symptoms (15), convenience (39), health concerns (45), emotional well-being (49), social issues (23), and economic issues (22).

CONCLUSIONS

The systematic content identification process identified 10 QOL domains, which were important to patients with glaucoma. The majority of the items were identified from the patient-specific focus groups and semistructured interviews suggesting that the existing PRO instruments do not adequately address QOL issues relevant to individuals with glaucoma.

Rasch analysis of the Student Refractive Error and Eyeglass Questionnaire

PURPOSE

To evaluate and refine a newly developed instrument, the Student Refractive Error and Eyeglasses Questionnaire (SREEQ), designed to measure the impact of uncorrected and corrected refractive error on vision-related quality of life (VRQoL) in school-aged children.

METHODS

A 38-statement instrument consisting of two parts was developed: part A relates to perceptions regarding uncorrected vision and part B relates to perceptions regarding corrected vision and includes other statements regarding VRQoL with spectacle correction. The SREEQ was administered to 200 Native American 6th- through 12th-grade students known to have previously worn and who currently require eyeglasses. Rasch analysis was conducted to evaluate the functioning of the SREEQ. Statements on parts A and B were analyzed to examine the dimensionality and constructs of the questionnaire, how well the items functioned, and the appropriateness of the response scale used.

RESULTS

Rasch analysis suggested two items be eliminated and the measurement scale for matching items be reduced from a four-point response scale to a three-point response scale. With these modifications, categorical data were converted to interval-level data to conduct an item and person analysis. A shortened version of the SREEQ was constructed with these modifications, the SREEQ-R, which included the statements that were able to capture changes in VRQoL associated with spectacle wear for those with significant refractive error in our study population.

CONCLUSIONS

Although part B of the SREEQ appears to have a less-than-optimal reliability to assess the impact of spectacle correction on VRQoL in our student population, it is able to detect statistically significant differences from pretest to posttest on both the group and individual levels to show that the instrument can assess the impact that glasses have on VRQoL. Further modifications to the questionnaire, such as those included in the SREEQ-R, could enhance its functionality.

Quality assessment of ophthalmic questionnaires: review and recommendations

PURPOSE

The aim of this article was to systematically review all the available ophthalmic patient-reported outcome (PRO) instruments (questionnaires) that demonstrated interval measurement properties to identify the instruments with the highest psychometric quality for use in different eye diseases and conditions.

METHODS

An extensive literature review was carried out to identify all existing ophthalmic PRO instruments. Instruments were then excluded if they did not have demonstrable interval measurement properties; the remaining instruments were reviewed. The quality of the following psychometric properties was assessed: content development (initial item development process), performance of the response scale, dimensionality (whether the instrument measures a single construct), measurement precision, validity (convergent, concurrent, discriminant, and known groups), reliability (test-retest), targeting (whether the items are appropriate [e.g., difficulty level] for the population), differential item functioning (whether subgroups of people respond differently to an item), and responsiveness.

RESULTS

The search identified 48 PRO instruments that demonstrated interval measurement properties, and these were relevant to nine applications: glaucoma, dry eye, refractive errors, cataract, amblyopia and strabismus, macular diseases, adult low vision, children low vision, and others. These instruments were evaluated against the psychometric property quality criteria and were rated for quality based on the number of criteria met.

CONCLUSIONS

This review provides a descriptive catalog of ophthalmic PRO instruments to inform researchers and clinicians on the choice of the highest-quality PRO instrument suitable for their purpose.

The impact of structural and functional parameters in glaucoma patients on patient-reported visual functioning

BACKGROUND

To evaluate the impact of structural changes of the retinal nerve fiber layer (RNFL), and visual field loss, on functional impairment assessed by patient-reported visual functioning in glaucoma.

METHODS

Patients with glaucomatous optic nerve damage were enrolled in this cross-sectional study. Peripapillary RNFL thickness was obtained with spectral-domain optical coherence tomography (SD-OCT). Function was assessed by patient-reported visual functioning using the Rasch-calibrated Glaucoma Activity Limitation 9 (GAL-9) questionnaire and standard automated perimetry. The impact of peripapillary RNFL loss on functional impairment was analyzed with correlation and linear regression analyses.

RESULTS

A total of 176 eyes from 88 glaucoma patients were included. The SD-OCT assessed temporal-superior and temporal-inferior RNFL sector of the worse eye revealed significant correlation with the GAL-9 scores (r=-0.298, p=0.011 and r=-0.251, p=0.033, respectively). In mutivariate regression analysis, the best predictors for patient-reported visual functioning were visual acuity of the better eye and mean defect of the worse eye (R(2)=0.334), while structural parameters could not enhance the prediction of GAL-9 scores.

CONCLUSIONS

Self-reported visual functioning of patients with glaucoma is better predicted by visual performance data than structural parameters. However, some structural changes of the worse eye are significantly correlated with patient-reported visual functioning.

Development of a vision-targeted health-related quality of life item measure

PURPOSE

To develop a vision-targeted health-related quality of life (HRQOL) measure for the NIH Toolbox for the Assessment of Neurological and Behavioral Function.

METHODS

We conducted a review of existing vision-targeted HRQOL surveys and identified color vision, low luminance vision, distance vision, general vision, near vision, ocular symptoms, psychosocial well-being, and role performance domains. Items in existing survey instruments were sorted into these domains. We selected non-redundant items and revised them to improve clarity and to limit the number of different response options. We conducted 10 cognitive interviews to evaluate the items. Finally, we revised the items and administered them to 819 individuals to calibrate the items and estimate the measure's reliability and validity.

RESULTS

The field test provided support for the 53-item vision-targeted HRQOL measure encompassing 6 domains: color vision, distance vision, near vision, ocular symptoms, psychosocial well-being, and role performance. The domain scores had high levels of reliability (coefficient alphas ranged from 0.848 to 0.940). Validity was supported by high correlations between National Eye Institute Visual Function Questionnaire scales and the new-vision-targeted scales (highest values were 0.771 between psychosocial well-being and mental health, and 0.729 between role performance and role difficulties), and by lower mean scores in those groups self-reporting eye disease (F statistic with p < 0.01 for all comparisons except cataract with ocular symptoms, psychosocial well-being, and role performance scales).

CONCLUSIONS

This vision-targeted HRQOL measure provides a basis for comprehensive assessment of the impact of eye diseases and treatments on daily functioning and well-being in adults.

Rasch analysis of Impact of Vision Impairment for Children questionnaire

PURPOSE

To validate the Indian-translated Impact of Vision Impairment for Children (IVI_C), a vision-related quality of life (VRQoL) instrument, and to investigate the effect of sociodemographic and ocular characteristics on VRQoL.

METHODS

The 24-item IVI_C was administered face to face to 221 children with vision impairment (VI) (mean age, 12.6 years; male, 68%) referred to the Vision Rehabilitation Centres. Rasch analysis was used to investigate the IVI_C for key indices such as measurement precision as measured by person separation (minimum recommended value, 2.0), unidimensionality (i.e., whether all the items contribute toward measurement of a single underlying construct as assessed by item fit and principal component analysis of residuals), targeting of items to participants' VRQoL (i.e., matching of item difficulty to participant ability; ideal targeting, <1.0 logits). Univariate analysis was performed to determine if the person scores of IVI_C were significantly different across participant subgroups stratified by sociodemographic and ocular characteristics, including the severity of VI.

RESULTS

The IVI_C showed misfit to the model and lacked unidimensionality. Principal component analysis confirmed the presence of an additional construct, mobility, but it did not possess adequate person separation when assessed individually. Deleting the mobility-related items restored unidimensionality, but additional items misfit, necessitating item reduction. Finally, a 17-item IVI_C possessed good measurement precision (person separation, 2.04), was unidimensional (albeit not purely), and consisted of items that fit the Rasch model and were well targeted to the participants' VRQoL (targeting 0.76 logits). There was no statistically significant difference in the VRQoL across subgroups stratified by age, sex, type of school, cause of VI, duration of vision loss, and severity of VI (p > 0.05 for all).

CONCLUSIONS

The revised 17-item IVI_C is shorter and has better psychometric properties than the original version in school-aged children with VI in India, and the responses are unrelated to sociodemographic and clinical variables. Although it has the potential for use in cross-sectional and outcomes research in children with VI, caution should be exercised while interpreting the 17-item IVI_C scores given the presence of slight multidimensionality.

Validity of LupusQoL-China for the assessment of health related quality of life in Chinese patients with systemic lupus erythematosus

Objectives

To adapt and assess the validity and reliability of LupusQoL for use in Chinese patients with systemic lupus erythematosus (SLE).

Methods

Debriefing interviews of subjects with SLE guided the language modifications of the tool. The process of adaptation proceeded according to the guideline and pre-testing results of LupusQoL-China. 220 SLE patients completed LupusQoL-China and a generic preference-based measurement of health EuroQoL scale (EQ-5D), and 20 patients repeated them after 2 weeks. Internal consistency (ICR) and test-retest (TRT) reliability, convergent and discriminant validity were examined. Factor analysis and Rasch analysis were performed.

Results

The mean (SD) age of the 208 subjects with SLE was 33.93 (±9.19) years. ICR and TRT of the eight domains ranged from 0.811 to 0.965 and 0.836 to 0.974, respectively. The LupusQoL-China domains demonstrated substantial evidence of construct validity when compared with equivalent domains on the EQ-5D (physical health and usual activities r = −0.63, pain and pain/discomfort r = −0.778, emotional health and anxiety/depression r = −0.761, planning and usual activities r = −0.560). Most LupusQoL-China domains could discriminate patients with varied disease activities and end-organ damage (according to SELENA-SLEDAI and SLICC-DI). The principal component analysis revealed six factors, and confirmatory factor analysis result of which is similar to eight factors model.

Conclusions

These results provide evidence that the LupusQoL-China is valid as a disease-specific HRQoL assessment tool for Chinese patients with SLE.

Evaluating the effectiveness of multidisciplinary low-vision rehabilitation

PURPOSE

To objectively evaluate the changes in vision-specific quality of life (QoL) after multidisciplinary low-vision rehabilitation at the Royal Society for the Blind Low-Vision Clinic.

METHODS

The standard care model at the Royal Society for the Blind Low-Vision Clinic is optical management at the initial assessment, with subsequent referral to multidisciplinary services as required. Participants completed the Impact of Vision Impairment Questionnaire (IVI) and Veterans Affairs Low-Vision Visual Functioning Questionnaire (VA LV VFQ-48) before initial assessment, at 30 days (to assess the outcome of optical management) and at 3 months follow-up (to assess the outcome of multidisciplinary services).

RESULTS

Seventy-one participants completed the study. Using the VA LV VFQ-48, an improvement (p < 0.05) was seen at 30 days follow-up in overall visual ability, and the reading, visual information, and visual motor subscores. However, at 3 months follow-up, all subscores were not significantly different from pre-rehabilitation levels. In contrast, for the IVI, there was no improvement in both the overall score and the mobility subscale at 30 days follow-up, but a significant improvement at 3 months follow-up. Greater improvements in visual function were seen for those with low vision (<20/60-20/200) compared with those with blindness, those aged >85 years compared with those aged 80 to 85 and <80 years, and those without glaucoma (visual motor subscore).

CONCLUSIONS

The VA LV VFQ-48 and IVI demonstrated improvements in QoL after low-vision rehabilitation. The timing of the observed changes varied between the two questionnaires, reflecting the different content of these instruments and the timing of delivery of multidisciplinary services, but also suggests that continued rehabilitation may be warranted to maintain a patient's QoL.

A randomized, single-center study of equivalence of 2 intraocular lenses used in cataract surgery

PURPOSE

To compare the outcomes of 2 intraocular lenses (IOLs) for the treatment of age-related cataracts.

DESIGN

Prospective, randomized trial.

PARTICIPANTS

Patients with age-related cataracts were recruited and randomized to receive phacoemulsification and implantation of either the AcrySof SA60AT lens (Alcon, Inc, Fort Worth, TX) or the low-cost Tecsoft Flex lens (Fred Hollows Foundation, Tilganga, Nepal). A total of 300 patients were available for description and analysis (148 in the AcrySof group and 152 in the Tecsoft group).

METHODS

Patients underwent phacoemulsification and implantation of the AcrySof SA60AT lens or the Tecsoft Flex lens. They were followed up and examined at baseline, 1 week, 1 month, 6 months, and 12 months after cataract surgery.

MAIN OUTCOME MEASURES

Uncorrected distance visual acuity (UDVA), best-corrected distance visual acuity (BDVA), incidence of posterior capsule opacification (PCO), Visual Function Index questionnaire results, and safety of the implanted IOLs.

RESULTS

No significant difference (P>0.05) was found in UDVA and BDVA after surgery between the 2 groups. The equivalence test of the 95% confidence intervals showed that both lenses had an equal improvement of UDVA and BDVA as well as similar rates of PCO after cataract surgery. There was no significant difference between the 2 groups with regard to visual functioning or the incidence of adverse surgical events during (P>0.05) or after (P>0.05) the surgery.

CONCLUSIONS

The Tecsoft Flex IOL is a low-cost suitable alternative that is similar to the AcrySof IOL in terms of safety and visual outcomes.

Item and response-category functioning of the Persian version of the KIDSCREEN-27: Rasch partial credit model

BACKGROUND

The purpose of the study was to determine whether the Persian version of the KIDSCREEN-27 has the optimal number of response category to measure health-related quality of life (HRQoL) in children and adolescents. Moreover, we aimed to determine if all the items contributed adequately to their own domain.

FINDINGS

The Persian version of the KIDSCREEN-27 was completed by 1083 school children and 1070 of their parents. The Rasch partial credit model (PCM) was used to investigate item statistics and ordering of response categories. The PCM showed that no item was misfitting. The PCM also revealed that, successive response categories for all items were located in the expected order except for category 1 in self- and proxy-reports.

CONCLUSIONS

Although Rasch analysis confirms that all the items belong to their own underlying construct, response categories should be reorganized and evaluated in further studies, especially in children with chronic conditions.

Andhra Pradesh Eye Disease Study - Visual Function Questionnaire: further improvements in psychometric properties using Rasch analysis

PURPOSE

Previous Rasch analysis of the Andhra Pradesh Eye Disease Study-Visual Function Questionnaire (APEDS-VFQ) lacked comprehensiveness, specifically, dimensionality (whether it measures single/multiple constructs). Therefore, using the Rasch model this study provides a detailed assessment of psychometric properties of the APEDS-VFQ.

METHODS

A total of 351 visually impaired adults (mean age, 43.3 years) were verbally administered the APEDS-VFQ. Rasch analysis was used to assess the psychometric properties of the instrument.

RESULTS

Participants could distinguish only three categories of difficulty, so response categories were reduced from five to three. A single item ("reading small prints in newspaper/magazines", infit mean square 1.54) misfit the model. The overall pattern of fit statistics for item and person measures suggested that the underlying construct (visual ability) is not unidimensional. When the items were grouped into subsets based on functional requirements (resolution, contrast sensitivity, illumination and peripheral vision) and separate person measures were estimated for each of these domains, the first principal component contained the visual ability and accounted for 72% of the variance. Item measure distributions could be divided into 18 strata, and item-separation reliability was 0.99. Person measures could be divided into three statistically distinct strata and the person-separation reliability was 0.81.

CONCLUSIONS

The APEDS-VFQ is a precise measure of visual ability in visually impaired adults in India. Similar to other visual function questionnaires developed for the Western population, our results demonstrate that visual ability is a two-factor composite latent variable; one dimension heavily influences reading and the other most heavily influences peripheral vision (mobility).

The importance of rating scales in measuring patient-reported outcomes

Background

A critical component that influences the measurement properties of a patient-reported outcome (PRO) instrument is the rating scale. Yet, there is a lack of general consensus regarding optimal rating scale format, including aspects of question structure, the number and the labels of response categories. This study aims to explore the characteristics of rating scales that function well and those that do not, and thereby develop guidelines for formulating rating scales.

Methods

Seventeen existing PROs designed to measure vision-related quality of life dimensions were mailed for self-administration, in sets of 10, to patients who were on a waiting list for cataract extraction. These PROs included questions with ratings of difficulty, frequency, severity, and global ratings. Using Rasch analysis, performance of rating scales were assessed by examining hierarchical ordering (indicating categories are distinct from each other and follow a logical transition from lower to higher value), evenness (indicating relative utilization of categories), and range (indicating coverage of the attribute by the rating scale).

Results

The rating scales with complicated question format, a large number of response categories, or unlabelled categories, tended to be dysfunctional. Rating scales with five or fewer response categories tended to be functional. Most of the rating scales measuring difficulty performed well. The rating scales measuring frequency and severity demonstrated hierarchical ordering but the categories lacked even utilization.

Conclusion

Developers of PRO instruments should use a simple question format, fewer (four to five) and labelled response categories.

A new look at the WHOQOL as health-related quality of life instrument among visually impaired people using Rasch analysis

PURPOSE

To examine the psychometric characteristics of the World Health Organization quality of life instrument-modified Indian version (modified WHOQOL) and its subscales in adults with visual impairment (VI) using Rasch analysis.

METHODS

Cross-sectional data were of people aged ≥40 years with VI (n = 1,333) who responded to the modified WHOQOL in the Andhra Pradesh Eye Disease Study, India. Rasch analysis was used to explore the instrument and its subscales for key indices such as measurement precision by person separation reliability, PSR (i.e., discrimination between strata of participants' health-related QOL [HRQOL], recommended minimum value 0.8), unidimensionality (i.e., measurement of a single construct), and targeting (i.e., matching of item difficulty to participants' HRQOL).

RESULTS

Rasch-guided iterative approach including category re-organization to enable threshold ordering and item deletion to overcome multidimensionality resulted in a unidimensional 9-item WHOQOL and a 6-item level of independence (LOI) subscale with adequate PSR (0.81 and 0.82, respectively). Targeting was sub-optimal for both (-1.58 logits for WHOQOL and -2.55 logits for the subscale). Remaining subscales were dysfunctional.

CONCLUSIONS

The WHOQOL and LOI subscale can be improved and shortened, and the Rasch-revised versions are likely to assess the HROQL of VI patients best because of their brevity, reliability, and unidimensionality.

Evaluation of the Adult Strabismus-20 (AS-20) questionnaire using Rasch analysis

PURPOSE

To further refine the Adult Strabismus 20 (AS-20) health-related quality of life (HRQOL) questionnaire using Rasch analysis.

METHODS

Rasch analysis was performed independently on the original AS-20 using the following steps: dimensionality, response ordering, local dependence, infit and outfit analyses, differential item functioning, subject targeting, and confirmatory dimensionality.

RESULTS

Two subscales were present in each of the original AS-20 subscales, for a total of 4 subscales, which were labeled "self-perception," "interaction," "reading function," and "general function." Response ordering was appropriate for 3 of the subscales but required reduction to 4 response options for the fourth subscale. No notable local dependence was found for any subscale. As a result of fit analysis, 2 items were removed, 1 each from 2 subscales. No significant differential item functioning was seen for sex or age. The resulting 5-item self-perception subscale and 4-item reading function subscale are reliable and target the adult strabismus patient cohort appropriately. The resulting 5-item interaction subscale and 4-item general function subscale have less than optimal reliability.

CONCLUSIONS

The AS-20 benefits from reduction to 4 subscales (self-perception, interaction, reading function, and general function) and reducing the response options in the general function subscale from 5 to 4 options. The refined AS-20 may prove to be even more responsive to HRQOL changes in adult strabismus following treatment or changes over time.

Using Rasch rating scale model to reassess the psychometric properties of the Persian version of the PedsQL™ 4.0 Generic Core Scales in school children

BACKGROUND

Item response theory (IRT) is extensively used to develop adaptive instruments of health-related quality of life (HRQoL). However, each IRT model has its own function to estimate item and category parameters, and hence different results may be found using the same response categories with different IRT models. The present study used the Rasch rating scale model (RSM) to examine and reassess the psychometric properties of the Persian version of the PedsQL™ 4.0 Generic Core Scales.

METHODS

The PedsQL™ 4.0 Generic Core Scales was completed by 938 Iranian school children and their parents. Convergent, discriminant and construct validity of the instrument were assessed by classical test theory (CTT). The RSM was applied to investigate person and item reliability, item statistics and ordering of response categories.

RESULTS

The CTT method showed that the scaling success rate for convergent and discriminant validity were 100% in all domains with the exception of physical health in the child self-report. Moreover, confirmatory factor analysis supported a four-factor model similar to its original version. The RSM showed that 22 out of 23 items had acceptable infit and outfit statistics (<1.4, >0.6), person reliabilities were low, item reliabilities were high, and item difficulty ranged from -1.01 to 0.71 and -0.68 to 0.43 for child self-report and parent proxy-report, respectively. Also the RSM showed that successive response categories for all items were not located in the expected order.

CONCLUSIONS

This study revealed that, in all domains, the five response categories did not perform adequately. It is not known whether this problem is a function of the meaning of the response choices in the Persian language or an artifact of a mostly healthy population that did not use the full range of the response categories. The response categories should be evaluated in further validation studies, especially in large samples of chronically ill patients.

Technology and everyday functioning in people with intellectual disabilities: a Rasch analysis of the Everyday Technology Use Questionnaire (ETUQ)

BACKGROUND

As people with intellectual disabilities (ID) today live integrated in society and use different technological artefacts and services in their everyday life, more in-depth evaluation methods are crucial to detect strengths and limitations of their everyday technology use. The Everyday Technology Use Questionnaire (ETUQ) was originally designed to investigate the extent to which older adults with cognitive limitations can use the everyday technology that is of relevance to them. The purpose of this study was to explore and evaluate evidence of the validity of ETUQ among adult persons with ID.

METHODS

The original 93-item ETUQ was used to interview 120 adult participants with ID, recruited from a region in northern Sweden. A Rasch model was used to analyse the psychometric properties of the rating scale, scale validity, person response validity and person separation.

RESULTS

The ETUQ rating scale displayed sound psychometric properties when used with this sample. The goodness-of-fit statistics showed that 15 (16%) of the 93 items demonstrated higher values than expected. A step-by-step removal process of items not demonstrating fit to the model resulted in an ETUQ version with 46 items (49%) that met all the criteria for scale validity. Fifteen participants (12%), primarily with mild ID, still demonstrated a higher number of unexpected responses included in ETUQ.

CONCLUSIONS

The results of this study indicate that the ETUQ generates a valid measure of perceived difficulty in using everyday technology including adult persons with ID.

Derivation of the acceptance and self-worth adjustment scale

PURPOSE

The original 55-item Nottingham Adjustment Scale (NAS) is a first generation self-report instrument constructed using classical test theory to evaluate adjustment to vision loss. This study assesses the function of the NAS using Rasch analysis in a sample of adults with visual impairment and presents a revised second-generation instrument.

METHODS

Ninety-nine subjects with established vision loss (median onset 5 years) were administered the NAS. Rasch analysis was performed to: (1) determine optimum response scale function, (2) aid item reduction, (3) determine reliability indices and item targeting, (4) assess unidimensionality using Rasch-based principal component analysis, (5) assess differential item functioning (notable defined as >1.0 logit), and (6) formulate person measures to correlate with Geriatric Depression Scale scores and distance visual acuity to indicate convergent and discriminant validity, respectively.

RESULTS

Response categories exhibited underutilization, which when repaired improved response scale functioning and ordered structural calibrations. Misfitting items were removed iteratively until all items had mean-square infit and outfit values of 0.70 to 1.30. However, principal component analysis confirmed insufficient unidimensionality (two contrasts identified, eigenvalues 2.4 and 2.3). Removal of these contrasts and two further iterations restored unidimensionality. Despite item mistargeting (1.58 logits), the revised 19-item instrument demonstrated good person (0.85) and item (0.96) reliability coefficients, good convergent and discriminant validity, and no systematic differential item functioning. The resultant 19-item instrument was termed the Acceptance and Self-Worth Adjustment Scale (AS-WAS).

CONCLUSIONS

In those with established vision loss, the 19-item Acceptance and Self-Worth Adjustment Scale is a reliable and valid instrument that estimates the level of adjustment concerned with acceptance, attitudes, self-esteem, self-efficacy, and locus of control. An additional measure of depression and anxiety is recommended to assess adjustment in a broader sense. Confirmation of item ordering is required if to be used in those with newly acquired vision loss.