The lower-limb tasks questionnaire: an assessment of validity, reliability, responsiveness, and minimal important differences

OBJECTIVES

To develop a questionnaire that focuses only on physical tasks related to lower-limb function and, within that questionnaire, to explore the psychometric properties of a series of questions that are related specifically to activities of daily living (ADLs) and a series of activities more often associated with recreation.

DESIGN

Inception cohort.

SETTING

Private practice.

PARTICIPANTS

Data were primarily from patients who had experienced a lower-limb injury that would typically involve rehabilitation up to 6 weeks.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Through 5 studies, the following psychometric qualities were evaluated: content and factor validity, construct and concurrent validity, test-retest reliability (intraclass correlation coefficient [ICC], typical error), responsiveness (effect size, standardized response mean, Guyatt's responsiveness statistic), and the minimum important difference (distribution, anchor-based approaches).

RESULTS

Factor analysis supported the theoretical perspective that ADLs and recreational activities can be treated as different domains within the construct of function. Internal consistency was high (Cronbach alpha: ADLs, .91; recreational activities, .95) and the 2 domains explained a moderate level of the response variance (61%). In the ADL domain, 7 tasks had greater than 80% of participants regarding them as having some importance. For recreational activities, 6 tasks had 79% or more of participants regarding them as having some importance. Both domains were moderately correlated to actual performance of tasks (r = .62, r = .72), and to other questionnaires used for lower-limb injuries (r range, .51-.86). The floor and ceiling effects of the domains followed an expected pattern that could be related to the loading forces experienced on the injured limb during activities. The reliability of the 2 domains was high (ICCs >.95), and the Bland-Altman plots showed that the distribution of error across the range of scores was random with low bias scores (<1.0 point). Typical error scores were 2 points for each domain. All measures of responsiveness were high (1.2-6.7). Measures of the minimal important difference varied (3-10 points) according to the methodologic approach used.

CONCLUSIONS

The questionnaire possesses good factor structure and composition, relates well with other measures of function, differentiates patients with regard to certain characteristics or processes known to occur after injury, shows high levels of reliability and responsiveness, and shows evidence of good minimal important difference scores. The findings support the use of the questionnaire in both clinical scenarios and in research.