Construct validity of the late life function and disability instrument for adults with chronic conditions

OBJECTIVES: To evaluate the validity of the late life function and disability instrument (LLFDI) when applied to adults aged 44-65 years with chronic conditions. DESIGN: We applied a convergent cross-sectional construct validity design to examine the association between the LLFDI subscales and the medical outcomes study (MOS) 36-Item Health Survey Physical Component Score (SF36 PCS), MOS Physical Functioning scale (PF10), 2-minute walk distance (2MWD) and 8-foot walk test (8FWT). PARTICIPANTS: Our sample consisted of 174 community-dwelling adults age 45-65 years with one or more chronic conditions. SETTING: Participants were enrolled at a multidisciplinary family health practice. RESULTS: The LLFDI function correlated strongly with the PF10 (r = 0.84) and moderately with the 2MWD (r = 0.53) and 8FWT (r = -0.48). The LLFDI disability limitation correlated moderately with the SF36 PCS, 2MWD and 8FWT (r = 0.67, 0.45, -0.32, respectively). The LLFDI disability frequency correlated moderately with the SF36 PCS, 2MWD and 8FWT (r = 0.44, 0.33, -0.31). Ninety-five percent confidence intervals on all correlation coefficients excluded zero. CONCLUSION: Cross-sectional convergent validity of the LLFDI was supported when applied to adults 45-65 years of age with chronic conditions.