title: Surrogate screening models for the low physical activity criterion of frailty.
abstract: OBJECTIVE
  Low physical activity, one of five criteria in a validated clinical phenotype of frailty, is assessed by a standardized, semiquantitative questionnaire on up to 20 leisure time activities. Because of the time demanded to collect the interview data, it has been challenging to translate to studies other than the Cardiovascular Health Study (CHS), for which it was developed. Considering subsets of activities, we identified and evaluated streamlined surrogate assessment methods and compared them to one implemented in the Women's Health and Aging Study (WHAS).
  
  
  METHODS
  Using data on men and women ages 65 and older from the CHS, we applied logistic regression models to rank activities by "relative influence" in predicting low physical activity.We considered subsets of the most influential activities as inputs to potential surrogate models (logistic regressions). We evaluated predictive accuracy and predictive validity using the area under receiver operating characteristic curves and assessed criterion validity using proportional hazards models relating frailty status (defined using the surrogate) to mortality.
  
  
  RESULTS
  Walking for exercise and moderately strenuous household chores were highly influential for both genders. Women required fewer activities than men for accurate classification. The WHAS model (8 CHS activities) was an effective surrogate, but a surrogate using 6 activities (walking, chores, gardening, general exercise, mowing and golfing) was also highly predictive.
  
  
  CONCLUSIONS
  We recommend a 6 activity questionnaire to assess physical activity for men and women. If efficiency is essential and the study involves only women, fewer activities can be included.
authors: Division of Biostatistics, Keck School of Medicine, University of Southern California, 1540 Alcazar Street, CHP-220, Los Angeles, CA 90089-9011, USA. eckel@usc.edu
authors: Sandrah P
authors: SP
authors: Eckel
authors: Karen
authors: K
authors: Bandeen-Roche
authors: Paulo H M
authors: PH
authors: Chaves
authors: Linda P
authors: LP
authors: Fried
authors: Thomas A
authors: TA
authors: Louis
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D015331:Cohort Studies; D015444:Exercise; D005260:Female; D005500:Follow-Up Studies; D016330:Frail Elderly; D015577:Geriatric Assessment / Q000379:methods*; D006801:Humans; D007899:Leisure Activities; D016015:Logistic Models; D008297:Male; D009043:Motor Activity; D011446:Prospective Studies; D011795:Surveys and Questionnaires; D016387:Women's Health