Measures of cognitive functioning in the 1994-2000 Second Longitudinal Study of Aging.

Objectives: This report describes in detail the measures of cognitive functioning administered in the Second Longitudinal Study of Aging (LSOA II) and proposes a three-category cognitive impairment variable for analysts' use that is derived from the individual measures.

Methods: LSOA II self-respondents completed an 11-question cognitive functioning measure based on the Telephone Interview of Cognitive Status (TICS) instrument. Proxy respondents answered nine questions drawn from the short Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE). Using cut points provided in the literature as a guide, a single three-level categorical measure of cognitive impairment was created: probable, possible, and no cognitive impairment.

Results: The cognitive functioning measures administered in LSOA II retain many of the favorable psychometric properties of the original TICS and IQCODE. The constructed cognitive impairment (CI) variable demonstrates good construct validity, and prevalence rates are generally consistent with those from other published studies.

Conclusions: The categorical CI variable is easy to use and interpret and allows analysts the option of combining self- and proxy-respondent data in investigations of associations between CI and health outcomes, including continuing independence, progressive impairment, health care utilization patterns, and mortality.