title: Underestimation of disability in community-living older persons.
abstract: OBJECTIVE
  When ascertaining the occurrence of disability, long assessment intervals may be problematic because they do not account for the possibility of recovery or for deaths or losses to follow-up. Our objective was to compare the rates of disability obtained from single follow-up assessments with those obtained from monthly assessments for intervals up to 24 months.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  General community.
  
  
  METHODS
  Seven hundred fifty-four nondisabled persons, aged 70 and older, categorized into three groups according to their risk for disability (low, intermediate, and high).
  
  
  METHODS
  Participants were followed with monthly telephone interviews to determine the occurrence of disability in one or more of four key activities of daily living (ADLs).
  
  
  RESULTS
  For each risk group, the rates of disability obtained from monthly assessments of ADL function (cumulative disability) were considerably greater than those obtained from single follow-up assessments (prevalent disability). These differences in rates increased progressively as the length of the assessment interval increased. For example, the cumulative and prevalence rates of disability in participants in the intermediate risk group were 0.24 and 0.11 at 6 months, 0.36 and 0.20 at 12 months, 0.46 and 0.16 at 18 months, and 0.53 and 0.20 at 24 months, respectively. Although the overall rates were lower, the results for persistent disability, defined as a new disability that was present for at least 2 consecutive months, were similar. Although these differences in rates were attributable almost exclusively to recovery from disability in the first 6 months, they were due increasingly to deaths and losses to follow-up over the next 18 months, particularly in participants in the high-risk group.
  
  
  CONCLUSIONS
  The occurrence of disability is substantially underestimated by longitudinal studies with long assessment intervals. More frequent assessments of functional status could lead to an improved understanding of the course and overall burden of disability in community-living older persons.
authors.affiliation: Departments of Internal Medicine and Epidemiology and Public Health Yale University School of Medicine, New Haven, Connecticut 06504, USA.gill@ynhh.org
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Gill
authors.forename: Susan E
authors.initials: SE
authors.lastname: Hardy
authors.forename: Christianna S
authors.initials: CS
authors.lastname: Williams
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D003625:Data Collection; D006233:Persons with Disabilities; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D008297:Male; D011446:Prospective Studies; D013223:Statistics as Topic