Pergamon SW. SC;. Med. Vol. 38, No. 7, 931-942. 1994 pp. Copyright c 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0277-9536194 $6.00 + 0.00 HOW MEASUREMENT TECHNIQUES INFLUENCE ESTIMATES OF DISABILITY IN OLDER POPULATIONS ALAN M. JETTE New England Research Institute, 9 Galen Street, Watertown, MA 02172, U.S.A Abstract-Measures of disability in activities of daily living (ADL) have become important indicators of the health of older persons. One fundamental decision in disability research is constructing or choosing a rating scale to measure ADL disability. Although there is growing consensus in the field on what ADLs to measure, there is little agreement on zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA how to measure ADL disability. This study compares the effect of scales that rate the presence of difficulty, use or human assistance and use of any type of assistance to perform seven different ADLs on prevalence estimates of disability in a probability sample of 1818 adults 70 years of age and older living in the six New England states. Results reveal that different disability rating scales can have a dramatic impact on prevalence estimates of disability in older populations. Measures that used the ‘difficulty’ scale produced disability estimates from 1.2 to 5 times greater than estimates from the ‘human assistance’ scale. The effect of rating scales was associated with respondents’ age, social factors, and health status. Effects also varied substantially across different ADLs. Researchers need to make careful choices of the disability ratings scales and use caution in drawing inter-study comparisons where different scaling methods were employed. Ke)t wordsdisability, aging, survey research INTRODUCTION Measures of disability in ‘activities of daily living’ (ADL) and ‘instrumental activities of daily living’ (IADL) have become important indicators of the health status of older persons [l]. Measures of disabil- ity are being used or have been proposed for use in determining compensation to health providers, pre- dicting patient prognosis, planning placement de- cisions, establishing qualifications for insurance benefits, predicting health service utilization, and evaluating health care treatment effectiveness [2, 3, 21-231. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Disability refers the consequences on the person’s to act in typical in society. to the basic of everyday life, such eating, bathing, dressing, of range of life of disability in of arbitrary rating scales. in the literature and in constructing or using a disability measure is how each ADL or IADL in the measure to be rated scored. Scales designed rate individual or IADL activities take of difficulty in performing it is to perform activity; of assistance or dependency : or not a or needs assistance to perform an activity; or not is performed. A of depen- dence if person needs assistance whether s/he uses be defined in a of different ways within a dependency scale. Assistance can include human as cane or adaptive or both. of different rating approaches. The most frequently a dependence rating is the Katz of Daily Living Scale [4] which assesses personal assistance is received in eating, to include both mechanical and personal help A widely used example difficulty rating approach Nagi’s physical performance of difficulty in performing physical activities [l I]. Other as those in the 1984 in their measure of disability [12]. Choices to use depend as well as of the researcher analyst in the population of disability statistics [14]. The apparent rationale for interpreting them 937