Job strain and trajectories of change in episodic memory before and after retirement: results from the Health and Retirement Study

BACKGROUND

We examined indicators of job strain in relation to level and change in episodic memory in the years leading up to as well as following retirement.

METHODS

Our analyses centre on 3779 individuals from the nationally representative Health and Retirement Study (baseline age 57.3 years) who reported gainful employment in an occupation for 10+ years prior to retirement, and who were assessed for episodic memory performance over up to 20 years (median 8 waves over 16 years). We used ratings from the Occupational Information Network (O*Net) to score occupations for job control and job demands, and to measure job strain (job demands/job control).

RESULTS

Controlling for sociodemographic characteristics, depressive symptoms, and cardiovascular disease, less job control and greater job strain were not significantly associated with change in episodic memory in the period leading up to retirement, but were associated with significantly poorer episodic memory at retirement and an accelerated rate of decline in episodic memory following retirement. The results did not vary for men and women or by self-employment status.

CONCLUSIONS

Job strain expressed mainly as low job control is linked to poorer episodic memory at retirement and more decline after retirement. Job characteristics appear to have implications for cognitive ageing independent of relevant confounds.

Coping with Job Loss and Reemployment: A Two-Wave Study

Using a national sample, this study investigated the effects of unemployed workers' coping resources and coping strategy use on reemployment after a three-month period. Based on previous research, it was expected that (1) three types of coping resources (self-esteem, social support, and financial resources) would be positively related to problem-focused coping with job loss, (2) coping resources would be negatively related to emotion-focused coping with job loss, (3) problem-focused coping would be positively related to reemployment, (4) problem-focused coping would be more strongly related to reemployment than emotion-focused coping, and (5) coping strategies would mediate the relationship between the availability of coping resources and obtaining reemployment. Results provided support for the direct effects of coping resources (self-esteem, social support, and, to some extent, financial resources) on coping strategies, and a direct effect of problem-focused coping on reemployment 3 months later. Self-esteem and social support were each indirectly related to subsequent employment status, mediated by problem-focused coping. In other words, individuals with higher levels of self-esteem and social support were not only more likely to engage in problem-focused coping, but having a higher level of self-esteem and social support was also associated with a higher likelihood of being reemployed three months later. Findings are pertinent for the design of more effective interventions that mitigate adverse effects of unemployment and facilitate a successful return to the workforce.

Factors associated with cognitive evaluations in the United States

OBJECTIVE

We aimed to explore factors associated with clinical evaluations for cognitive impairment among older residents of the United States.

METHODS

Two hundred ninety-seven of 845 subjects in the Aging, Demographics, and Memory Study (ADAMS), a nationally representative community-based cohort study, met criteria for dementia after a detailed in-person study examination. Informants for these subjects reported whether or not they had ever received a clinical cognitive evaluation outside of the context of ADAMS. Among subjects with dementia, we evaluated demographic, socioeconomic, and clinical factors associated with an informant-reported clinical cognitive evaluation using bivariate analyses and multivariable logistic regression.

RESULTS

Of the 297 participants with dementia in ADAMS, 55.2% (representing about 1.8 million elderly Americans in 2002) reported no history of a clinical cognitive evaluation by a physician. In a multivariable logistic regression model (n = 297) controlling for demographics, physical function measures, and dementia severity, marital status (odds ratio for currently married: 2.63 [95% confidence interval: 1.10-6.35]) was the only significant independent predictor of receiving a clinical cognitive evaluation among subjects with study-confirmed dementia.

CONCLUSIONS

Many elderly individuals with dementia do not receive clinical cognitive evaluations. The likelihood of receiving a clinical cognitive evaluation in elderly individuals with dementia associates with certain patient-specific factors, particularly severity of cognitive impairment and current marital status.

Mental work demands, retirement, and longitudinal trajectories of cognitive functioning

Age-related changes in cognitive abilities are well-documented, and a very important indicator of health, functioning, and decline in later life. However, less is known about the course of cognitive functioning before and after retirement and specifically whether job characteristics during one's time of employment (i.e., higher vs. lower levels of mental work demands) moderate how cognition changes both before and after the transition to retirement. We used data from n = 4,182 (50% women) individuals in the Health and Retirement Study, a nationally representative panel study in the United States, across an 18 year time span (1992-2010). Data were linked to the O*NET occupation codes to gather information about mental job demands to examine whether job characteristics during one's time of employment moderates level and rate of change in cognitive functioning (episodic memory and mental status) both before and after retirement. Results indicated that working in an occupation characterized by higher levels of mental demands was associated with higher levels of cognitive functioning before retirement, and a slower rate of cognitive decline after retirement. We controlled for a number of important covariates, including socioeconomic (education and income), demographic, and health variables. Our discussion focuses on pathways through which job characteristics may be associated with the course of cognitive functioning in relation to the important transition of retirement. Implications for job design as well as retirement are offered.

The apolipoprotein E genotype predicts longitudinal transitions to mild cognitive impairment but not to Alzheimer's dementia: findings from a nationally representative study

OBJECTIVE

The ε4 allele of the apolipoprotein E (APOE) genotype is the most widely accepted genetic risk factor for Alzheimer's dementia (AD), but findings on whether it is a risk factor for the AD prodrome, mild cognitive impairment (MCI), have been inconsistent. In a prospective longitudinal design, we investigated (a) whether transitions to MCI and other forms of neurocognitive impairment without dementia (CIND) are more frequent among normal ε4 carriers than among noncarriers and (b) whether subsequent transitions to AD from MCI and from other forms of CIND are more frequent among ε4 carriers than among noncarriers.

METHOD

The frequency of the ε4 allele was studied in older adults (mean age > 70), who had participated in two or more waves of neuropsychological testing and diagnosis in the Aging, Demographics, and Memory Study (ADAMS) of the United States Department of Health and Human Services, National Institutes of Health, National Institute on Aging's Health and Retirement Study, conducted by the University of Michigan. The association between ε4 and longitudinal transitions to specific types of CIND and dementia can be determined with this data set.

RESULTS

Epsilon 4 increased the rate of progression from normal functioning to MCI (58% of new diagnoses were carriers) but not to other forms of CIND. The rate of progression to AD from MCI or from other forms of CIND was not increased by ε4.

CONCLUSIONS

The results support the hypothesis that ε4 is a risk factor for transitions from normal functioning to MCI but not for subsequent transitions to AD. In the ADAMS sample, the reason ε4 is elevated in AD individuals is because it is already elevated in MCI individuals, who are the primary source of new AD diagnoses.

What do parents have to do with my cognitive reserve? Life course perspectives on twelve-year cognitive decline

BACKGROUND/AIMS

To examine the cognitive reserve hypothesis by comparing the contribution of early childhood and life course factors related to cognitive functioning in a nationally representative sample of older Americans.

METHODS

We examined a prospective, national probability cohort study (Health and Retirement Study; 1998-2010) of older adults (n=8,833) in the contiguous 48 United States. The main cognitive functioning outcome was a 35-point composite of memory (recall), mental status, and working memory tests. The main predictors were childhood socioeconomic position (SEP) and health, and individual-level adult achievement and health.

RESULTS

Individual-level achievement indicators (i.e., education, income, and wealth) were positively and significantly associated with baseline cognitive function, while adult health was negatively associated with cognitive function. Controlling for individual-level adult achievement and other model covariates, childhood health presented a relatively small negative, but statistically significant association with initial cognitive function. Neither individual achievement nor childhood SEP was statistically linked to decline over time.

CONCLUSIONS

Cognitive reserve purportedly acquired through learning and mental stimulation across the life course was associated with higher initial global cognitive functioning over the 12-year period in this nationally representative study of older Americans. We found little supporting evidence that childhood economic conditions were negatively associated with cognitive function and change, particularly when individual-level achievement is considered.

Functional limitations in older adults who have cognitive impairment without dementia

OBJECTIVE

To characterize the prevalence of functional limitations among older adults with cognitive impairment without dementia (CIND).

METHODS

Secondary data analysis was performed using the Aging, Demographics, and Memory Study data set. A total of 856 individuals aged ≥ 71 years were assigned to 3 diagnostic cognitive categories. A questionnaire was completed by a proxy informant regarding functional limitations for 744 of the 856 respondents.

RESULTS

Of the 744 patients, 263 (13.9%) had dementia, 201 (21.3%) had CIND, and 280 (64.8%) had normal cognition. Informants reported ≥1 instrumental activities of daily living (ADLs) limitation in 45% of the patients with CIND compared to 13% of the patients with normal cognition and 85% of the patients with dementia (P < .001). The ADL impairments among individuals with CIND were primarily attributed to physical health problems (n = 41; 40%).

CONCLUSIONS

Many individuals with CIND have impairment in a range of complex and basic daily activities, largely due to physical health problems.

Can on-site childcare have detrimental work outcomes? Examining the moderating roles of family supportive organization perceptions and childcare satisfaction

Using organizational support theory as an overarching framework, we investigated the moderating roles of family supportive organization perceptions (FSOP) and childcare satisfaction on the relationship between type of childcare use (on-site vs. external) on one hand, and work engagement and job satisfaction on the other hand. We tested study hypotheses using data collected from staff and faculty members from a large public university in the Southern United States. Results from multiple regression analyses indicated that, compared with external childcare users, employees using on-site childcare were less engaged in and satisfied with their jobs when they (a) perceived their organization to be unsupportive toward their family life and (b) were dissatisfied with their childcare provider. Organizational implications emphasize the importance of integrating any on-site childcare program with a climate that openly acknowledges and cares for employees' family-related responsibilities and providing high-quality childcare services to employees.

Caring for individuals with dementia and cognitive impairment, not dementia: findings from the aging, demographics, and memory study

OBJECTIVES

To compare the characteristics and outcomes of caregivers of adults with dementia with those of caregivers of adults with cognitive impairment, not dementia (CIND).

DESIGN

Cross-sectional.

SETTING

In-home assessment for cognitive impairment and self-administered caregiving questionnaire.

PARTICIPANTS

One hundred sixty-nine primary family caregivers of participants in the Aging, Demographics, and Memory Study (ADAMS). ADAMS participants were aged 71 and older drawn from the nationally representative Health and Retirement Study.

MEASUREMENTS

Neuropsychological testing, neurological examination, clinical assessment, and medical history were used to assign a diagnosis of normal cognition, CIND, or dementia. Caregiving measures included caregiving time, functional limitations, depressive symptoms, physical and emotional strain, caregiving rewards, caregiver health, and demographic characteristics.

RESULTS

Dementia caregivers spent approximately 9 hours per day providing care, compared with 4 hours per day for CIND caregivers (P=.001). Forty-four percent of dementia caregivers exhibited depressive symptoms, compared with 26.5% of CIND caregivers (P=.03). Physical and emotional strains were similar in both groups of caregivers. Regardless of the strains, nearly all caregivers reported some benefits from providing care. Behavioral problems (P=.01) and difficulty with instrumental activities of daily living (P=.01) in persons with CIND partially explained emotional strain experienced by CIND caregivers. For those with dementia, behavioral problems predicted caregiver emotional strain (P<.001) and depressive symptoms (P=.01).

CONCLUSION

Although support services are available to dementia caregivers, CIND caregivers also expend considerable time and experience strains. The real caregiver burden of cognitive impairment in the U.S. population may therefore be greatly underestimated if people who have reached the diagnostic threshold for dementia are focused on exclusively.

Incidence of dementia and cognitive impairment, not dementia in the United States

OBJECTIVE

Estimates of incident dementia, and cognitive impairment, not dementia (CIND) (or the related mild cognitive impairment) are important for public health and clinical care policy. In this paper, we report US national incidence rates for dementia and CIND.

METHODS

Participants in the Aging, Demographic, and Memory Study (ADAMS) were evaluated for cognitive impairment using a comprehensive in-home assessment. A total of 456 individuals aged 72 years and older, who were not demented at baseline, were followed longitudinally from August 2001 to December 2009. An expert consensus panel assigned a diagnosis of normal cognition, CIND, or dementia and its subtypes. Using a population-weighted sample, we estimated the incidence of dementia, Alzheimer disease (AD), vascular dementia (VaD), and CIND by age. We also estimated the incidence of progression from CIND to dementia.

RESULTS

The incidence of dementia was 33.3 (standard error [SE], 4.2) per 1,000 person-years and 22.9 (SE, 2.9) per 1,000 person-years for AD. The incidence of CIND was 60.4 (SE, 7.2) cases per 1,000 person-years. An estimated 120.3 (SE, 16.9) individuals per 1,000 person-years progressed from CIND to dementia. Over a 5.9-year period, about 3.4 million individuals aged 72 and older in the United States developed incident dementia, of whom approximately 2.3 million developed AD, and about 637,000 developed VaD. Over this same period, almost 4.8 million individuals developed incident CIND.

INTERPRETATION

The incidence of CIND is greater than the incidence of dementia, and those with CIND are at high risk of progressing to dementia, making CIND a potentially valuable target for treatments aimed at slowing cognitive decline.

Vascular health, diabetes, APOE and dementia: the Aging, Demographics, and Memory Study

INTRODUCTION

Evidence from clinical samples and geographically limited population studies suggests that vascular health, diabetes and apolipoprotein epsilon4 (APOE) are associated with dementia.

METHODS

A population-based sample of 856 individuals aged 71 years or older from all contiguous regions of the United States received an extensive in-home clinical and neuropsychological assessment in 2001-2003. The relation of hypertension, diabetes, heart disease, stroke, medication usage, and APOE epsilon4 to dementia was modelled using adjusted multivariable logistic regression.

RESULTS

Treated stroke (odds ratio [OR] 3.8, 95% confidence interval [CI] 2.0, 7.2), untreated stroke (OR 3.5, 95% CI 1.7, 7.3), and APOE epsilon4 (OR 2.8, 95% CI 1.7, 4.5) all increased the odds of dementia. Treated hypertension was associated with lower odds of dementia (OR 0.5, 95% CI 0.3, 1.0). Diabetes and heart disease were not significantly associated with dementia. A significant interaction was observed between APOE epsilon4 and stroke (P = 0.001).

CONCLUSIONS

Data from the first dementia study that is representative of the United States population suggest that stroke, the APOE epsilon4 allele and their interaction are strongly associated with dementia.

Beyond work and family: a measure of work/nonwork interference and enhancement

Though early research on the work/nonwork interface was broader in scope, most recent research has focused on the interface between work and family. There is a need for an inclusive, validated measure of work/nonwork interference and enhancement that is appropriate for all workers regardless of their marital or family life status. The authors report here on 3 studies in which they develop a theoretically grounded and empirically validated multidimensional, bidirectional measure of work/nonwork interference and enhancement. All scale items refer to work/nonwork, whereas previous measures have mixed work/family and work/nonwork items or emphasize family roles in the nonwork domain. Quantitative analysis of the scale items yielded 17 items to measure work interference with personal life, personal life interference with work, work enhancement of personal life, and personal life enhancement of work. Confirmatory factor analyses and structural equation modeling results provide evidence for convergent, discriminant, and criterion-related validity for the scale from 2 large samples of workers (N = 540, N = 384) across multiple job types and organizations.

Age Differences in the Demand-Control Model of Work Stress: An Examination of Data From 15 European Countries

There have been many tests of Karasek's demand-control model of work stress. However, no studies have examined how the model may differentially apply to older versus younger workers. Due to age changes in cognitive processing, the psychological demands of jobs may interact differently with controls for younger versus older workers. Therefore, the study uses data from the Eurobarometer to examine how the demand-control model of work stress may function differently for older versus younger workers. The results indicate that different controls may in fact buffer different types of job demands for younger versus older workers. The findings reveal that only the interaction between problem solving and time to complete tasks was significant for younger workers. For older workers, however, the interactions between time deadlines and having sufficient time to complete tasks, autonomy, and the interaction between problem solving and schedule flexibility are significant predictors of self-reported stress.

Parental education and late-life dementia in the United States

We investigated the relation between parental education and dementia in the United States. Participants in the Aging, Demographics, and Memory Study were included, with information regarding parental education obtained from the Health and Retirement Study. The odds of dementia in elderly Americans whose mothers had less then 8 years of schooling were twice (95% CI, 1.1-3.8) that of individuals with higher maternal education, when adjusted for paternal education. Of elderly Americans with less educated mothers, 45.4% (95% CI, 37.4-53.4%) were diagnosed with dementia or ;;cognitive impairment, no dementia'' compared to 31.2% (95% CI, 25.0-37.4%) of elderly Americans whose mothers had at least an 8th grade education. The population attributable risk of dementia due to low maternal education was 18.8% (95% CI, 9.4-28.2%). The education of girls in a population may be protective of dementia in the next generation.

Prevalence of cognitive impairment without dementia in the United States

BACKGROUND

Cognitive impairment without dementia is associated with increased risk for disability, increased health care costs, and progression to dementia. There are no population-based prevalence estimates of this condition in the United States.

OBJECTIVE

To estimate the prevalence of cognitive impairment without dementia in the United States and determine longitudinal cognitive and mortality outcomes.

DESIGN

Longitudinal study from July 2001 to March 2005.

SETTING

In-home assessment for cognitive impairment.

PARTICIPANTS

Participants in ADAMS (Aging, Demographics, and Memory Study) who were age 71 years or older drawn from the nationally representative HRS (Health and Retirement Study). Of 1770 selected individuals, 856 completed initial assessment, and of 241 selected individuals, 180 completed 16- to 18-month follow-up assessment.

MEASUREMENTS

Assessments, including neuropsychological testing, neurologic examination, and clinical and medical history, were used to assign a diagnosis of normal cognition, cognitive impairment without dementia, or dementia. National prevalence rates were estimated by using a population-weighted sample.

RESULTS

In 2002, an estimated 5.4 million people (22.2%) in the United States age 71 years or older had cognitive impairment without dementia. Prominent subtypes included prodromal Alzheimer disease (8.2%) and cerebrovascular disease (5.7%). Among participants who completed follow-up assessments, 11.7% with cognitive impairment without dementia progressed to dementia annually, whereas those with subtypes of prodromal Alzheimer disease and stroke progressed at annual rates of 17% to 20%. The annual death rate was 8% among those with cognitive impairment without dementia and almost 15% among those with cognitive impairment due to medical conditions.

LIMITATIONS

Only 56% of the nondeceased target sample completed the initial assessment. Population sampling weights were derived to adjust for at least some of the potential bias due to nonresponse and attrition.

CONCLUSION

Cognitive impairment without dementia is more prevalent in the United States than dementia, and its subtypes vary in prevalence and outcomes.

Memory decline and depressive symptoms in a nationally representative sample of older adults: the Health and Retirement Study (1998-2004)

BACKGROUND/AIMS

Inconsistencies in the relationship between depression and cognitive decline may exist because the expected cognitive domains at risk have not been specified in previous study designs. We aimed to examine the relationship between depressive symptoms and verbal episodic memory functioning over time.

METHODS

Data from a prospective cohort study (Health and Retirement Study; 1998-2004; n = 18,465), a multistage national probability sample of older adults in the United States, were analyzed. Verbal learning and memory of a 10-word list learning task were the main outcomes. Depressive symptoms (Center for Epidemiologic Studies - Depression Scale) constituted the main predictor.

RESULTS

Depressive symptoms were associated with significantly lower immediate (-0.05; p < 0.001) and delayed (-0.06; p < 0.001) word list recall scores after controlling for demographics and baseline and time-varying cardiovascular disease risks and diseases.

CONCLUSIONS

In this US national study of older adults, elevated depressive symptoms were associated with declines in episodic learning and memory over time. These associations were little affected by the demographic or medical conditions considered in this study. The results suggest that learning and memory decline may be a long-term feature associated with depressive symptoms among the nation's older adult population.

Prevalence of dementia in the United States: the aging, demographics, and memory study

AIM

To estimate the prevalence of Alzheimer's disease (AD) and other dementias in the USA using a nationally representative sample.

METHODS

The Aging, Demographics, and Memory Study sample was composed of 856 individuals aged 71 years and older from the nationally representative Health and Retirement Study (HRS) who were evaluated for dementia using a comprehensive in-home assessment. An expert consensus panel used this information to assign a diagnosis of normal cognition, cognitive impairment but not demented, or dementia (and dementia subtype). Using sampling weights derived from the HRS, we estimated the national prevalence of dementia, AD and vascular dementia by age and gender.

RESULTS

The prevalence of dementia among individuals aged 71 and older was 13.9%, comprising about 3.4 million individuals in the USA in 2002. The corresponding values for AD were 9.7% and 2.4 million individuals. Dementia prevalence increased with age, from 5.0% of those aged 71-79 years to 37.4% of those aged 90 and older.

CONCLUSIONS

Dementia prevalence estimates from this first nationally representative population-based study of dementia in the USA to include subjects from all regions of the country can provide essential information for effective planning for the impending healthcare needs of the large and increasing number of individuals at risk for dementia as our population ages.

Latent variable analyses of age trends of cognition in the Health and Retirement Study, 1992-2004

The present study was conducted to better describe age trends in cognition among older adults in the longitudinal Health and Retirement Study (HRS) from 1992 to 2004 (N = 17,000). The authors used contemporary latent variable models to organize this information in terms of both cross-sectional and longitudinal inferences about age and cognition. Common factor analysis results yielded evidence for at least 2 common factors, labeled Episodic Memory and Mental Status, largely separable from vocabulary. Latent path models with these common factors were based on demographic characteristics. Multilevel models of factorial invariance over age indicated that at least 2 common factors were needed. Latent curve models of episodic memory were based on age at testing and showed substantial age differences and age changes, including impacts due to retesting as well as several time-invariant and time-varying predictors.

The Aging, Demographics, and Memory Study: Study Design and Methods

OBJECTIVE

We describe the design and methods of the Aging, Demographics, and Memory Study (ADAMS), a new national study that will provide data on the antecedents, prevalence, outcomes, and costs of dementia and "cognitive impairment, not demented" (CIND) using a unique study design based on the nationally representative Health and Retirement Study (HRS). We also illustrate potential uses of the ADAMS data and provide information to interested researchers on obtaining ADAMS and HRS data.

METHODS

The ADAMS is the first population-based study of dementia in the United States to include subjects from all regions of the country, while at the same time using a single standardized diagnostic protocol in a community-based sample. A sample of 856 individuals age 70 or older who were participants in the ongoing HRS received an extensive in-home clinical and neuropsychological assessment to determine a diagnosis of normal, CIND, or dementia. Within the CIND and dementia categories, subcategories (e.g. Alzheimer's disease, vascular dementia) were assigned to denote the etiology of cognitive impairment.

CONCLUSION

Linking the ADAMS dementia clinical assessment data to the wealth of available longitudinal HRS data on health, health care utilization, informal care, and economic resources and behavior, will provide a unique opportunity to study the onset of CIND and dementia in a nationally representative population-based sample, as well as the risk factors, prevalence, outcomes, and costs of CIND and dementia.

Does urinary incontinence affect middle-aged and older women's time use and activity patterns?

OBJECTIVE

To investigate the relationship between urinary incontinence and women's levels and hours of participation in 31 activities.

METHODS

A subset of panel members from the Health and Retirement Study completed the self-administered Consumption and Activities Mail Survey questionnaire in 2001. These data were linked with Health and Retirement Study 2000 data. Analyses were limited to 2,190 female Consumption and Activities Mail Survey self-respondents born in 1947 or earlier. Logistic regression was used to predict activity participation. Linear regression was used to predict the number of hours of participation.

RESULTS

The hypothesis that urinary incontinence affects women's time use and activity patterns was supported. Compared with the continent women, the incontinent women were less likely to have house cleaned, shopped, physically shown affection, or attended religious services in the recent past; and were more likely to have watched television or made music by singing or playing an instrument. Compared with continent activity participants, incontinent participants reported significantly fewer hours spent walking, communicating with friends and family by telephone or e-mail, working for pay, using a computer, and engaging in personal grooming and hygiene.

CONCLUSION

These findings substantiate prior work on the relationship between urinary incontinence and quality of life, and suggest a useful route for educating patients about the impact of urinary incontinence. Clinicians must be alert to opportunities for encouraging incontinent women to be active. It is also important to consider the implications for time use and activity patterns when advising patients about treatment and management options.

LEVEL OF EVIDENCE

II-2.

A lengthy look at the daily grind: time series analysis of events, mood, stress, and satisfaction

The present study investigated processes by which job stress and satisfaction unfold over time by examining the relations between daily stressful events, mood, and these variables. Using a Web-based daily survey of stressor events, perceived strain, mood, and job satisfaction completed by 14 university workers, 1,060 occasions of data were collected. Transfer function analysis, a multivariate version of time series analysis, was used to examine the data for relationships among the measured variables after factoring out the contaminating influences of serial dependency. Results revealed a contrast effect in which a stressful event associated positively with higher strain on the same day and associated negatively with strain on the following day. Perceived strain increased over the course of a semester for a majority of participants, suggesting that effects of stress build over time. Finally, the data were consistent with the notion that job satisfaction is a distal outcome that is mediated by perceived strain.