title: Triggered sampling could help improve longitudinal studies of persons with elevated mortality risk.
abstract: OBJECTIVE
  One approach to overcoming potential biased results, due to dropout from longitudinal clinical studies, is to capture additional data once a marker of health downturn is observed but before the patient leaves the study. We denote this study design feature as "triggered sampling" (TS).
  
  
  METHODS
  We formally define TS, describe some mechanisms for incorporating TS in longitudinal studies, and present the results from a 2-year longitudinal observational study of treatment preferences, measured on a 1-7 scale, of patients with advanced illness from cancer, congestive heart failure, or chronic obstructive pulmonary disease. We examined the utility of TS through multiple analyses, including mixed effects models.
  
  
  RESULTS
  One hundred forty-eight of 226 participants experienced at least one triggered interview. Those who did not drop out after their first trigger had no noticeable change in their mean preferences (6.20 pretrigger, 6.16 trigger, P=0.76), whereas those who dropped out after their first trigger did (6.29 pretrigger, 5.69 trigger, P=0.04). The mixed effects models conveyed similar results, providing support for the efficiency and efficacy of TS.
  
  
  CONCLUSIONS
  TS can help alleviate bias due to impending dropout and potentially be a valuable addition to the designs of longitudinal studies of persons with elevated mortality risk.
authors.affiliation: Department of Statistics & Actuarial Science, University of Waterloo, Waterloo, ON, Canada. jdubin@uwaterloo.ca
authors.forename: Joel A
authors.initials: JA
authors.lastname: Dubin
authors.forename: Ling
authors.initials: L
authors.lastname: Han
authors.forename: Terri R
authors.initials: TR
authors.lastname: Fried
mesh_terms: D000368:Aged; D015982:Bias; D002755:Choice Behavior; D002908:Chronic Disease / Q000401:mortality*; D003625:Data Collection / Q000379:methods*; D015340:Epidemiologic Research Design; D006801:Humans; D008020:Life Support Care / Q000523:psychology; D008137:Longitudinal Studies; D008875:Middle Aged; D015233:Models, Statistical; D010352:Patient Dropouts; D018401:Sample Size