Mohammed T. Abou-Saleh

106 PRINCIPLES AND PRACTICE OF GERIATRIC PSYCHIATRYCHOICE OF COMPARISON GROUPSThe counterpart of case identification is the designation ofcomparison groups and addresses the question, ‘‘long-termoutcomes of disorder X compared with what?’’ Comparisongroups provide benchmarks for interpreting measures of outcome.What comparison groups are appropriate depends, of course, onthe research question under investigation and includes, amongothers, samples of ‘‘normal’’ individuals, of individuals with otherpsychiatric or medical conditions, or population norms, ifavailable. Comparisons may also be made on the basis of somerisk factor (e.g. age of onset) or treatment of interest. What isimportant to remember when selecting comparison groups andinterpreting results is that members of the case, or target, groupmay differ from those of the comparison group in ways other thanthe disorder or risk factor of interest, and these ‘‘other ways’’ mayaccount for subsequent differences in outcome and course. Thus,it is important to assess whether comparison groups arecomparable to case groups on extraneous dimensions that couldinfluence outcomes.SAMPLE REPRESENTATIVENESS AND ATTRITIONThe representativeness of the sample at baseline and follow-upaddresses the question, ‘‘to what extent and to whom are resultsgeneralizable?’’ Most current long-term follow-up studies arebased on patient samples selected from hospitals, other treatmentsettings, clinician caseloads or case registries. Selection intotreatment, however, is not a random process 11 . Treatment rateshave been shown to vary by type of disorder 12 , social anddemographic characteristics of individuals 12,26 , historical period 13 ,service delivery system and country. In addition, within acatchment area, patients are sorted and filtered into differenttypes of treatment settings (e.g. public vs. private). Thus, the lifetrajectories of treated subjects may differ not only from those ofuntreated cases but also from those of patients treated indissimilar settings.More significant is the problem of sample attrition, whetherdue to death, inability to participate, refusal or failure to trace.This is because subjects lost to follow-up tend to differ insystematic ways from those who are located and interviewed 3,14 .Researchers often attempt to assess the type and degree of bias bycomparing respondents and non-respondents on baseline characteristics;however, as Kelsey et al. 3 note, ‘‘the only way toensure that bias stemming from loss to follow-up does not distortthe study results is to minimize losses through intensive efforts tolocate each cohort member’’ (p. 109). In addition, by reducingsample size, attrition reduces the statistical power of analyses toreliably detect outcome differences. With effort, several long-termfollow-up studies have successfully minimized sample attrition 15 ;the training and organizational strategies used have beensummarized 15,16 .MEASUREMENT OF OUTCOMESThe measurement of outcomes is clearly central to long-termfollow-up studies and raises the question, ‘‘on what dimensionsand how should outcomes be assessed?’’ Many different measuresof outcome have been used in follow-up studies, includingmeasures of symptomatology, hospitalization, role functioning,impairment of social relationships and recovery 1,17,18 . Reliance onsingle global indices of recovery have proved largely unsatisfactory.Such indices are not only difficult to compare across studiesbut also imply an overly uniform picture of subjects’ functioning.Subjects who fare poorly in one life domain (e.g. employment)often fare better in others (e.g. symptom profile) 18 , and suchdiscrepancies are masked by single global indicators of recovery.Even seemingly objective, domain-specific measures (e.g. unemploymentor rehospitalization rates) can be difficult to compareacross studies if they are influenced by setting specific economicconditions or social policies 4,19 .Sample attrition further complicates the measurement ofoutcomes. How should outcomes be assessed for subjects whoare deceased or unlocated at follow-up? Investigators often relyon informants and/or records to provide information. However,in addition to raising ethical considerations, informants not onlydiffer from subjects in their access to (and probably recall of)relevant information but also assess subjects’ status fromdifferent perspectives. Records, too, may not contain the dataof interest and, like informant reports, differ in perspective fromsubjects’ self-reports 3,26 . In light of such considerations, it isimportant to follow the advice of Bromet et al. 4 and ‘‘. . . becautious in comparing results across studies without carefullyascertaining both the definition of outcome and the criteriaused in implementing that definition’’ (p. 154) (see refs 5,17 forelaboration).MEASURES OF INTERVENING VARIABLESThe longer the time interval between baseline and follow-up, themore likely that intervening events and circumstances play a rolein determining outcome status. Measurement of such events andcircumstances addresses the question, ‘‘what are the interimprocesses and mechanisms that account for observed outcomes?’’Here prospective designs have an advantage over retrospectivecohort studies because measurement of potentially mediating andconfounding variables can be explicitly built into both baselineand follow-up data collection, and time intervals between followupscan be chosen with intervening mechanisms in mind.Retrospective cohort designs are more dependent on the availabilityof records and/or the recollections of subjects andinformants, which are vulnerable to recall and reportingbiases 3,20,21,23 . Problems associated with reporting and recall arenot avoided by prospective studies, however, especially whenintervals between follow-ups are long.PRACTICAL APPROACHES TO FOLLOW-UPSmith and Watts 27 provide a thorough summary of methods forlocating absent and deceased subjects. Their review of availableprocedures emphasizes the use of electronic databases as effectivemeans for identifying the location and vital status of lost subjects.Various tools for locating participants lost to follow-up arecurrently available.Sources for Locating Patients Assumed AliveThe US Postal Service is a convenient source of information wheninvestigators are faced with outdated addresses. Upon request, anupdated address can be obtained as long as the request is madewithin the year that the individual moved.Incorrect telephone numbers can be updated by contacting thetelephone operator for information on new telephone listings.Unlisted telephone numbers may be obtained, depending on thepolicy of the telephone company. White-page listings for theentire USA are available for purchase on compact disk (CD-ROM). Compact disks are updated yearly and are relativelyaffordable. Telephone numbers can also be updated by use of the