title: Constructing common cohorts from trials with overlapping eligibility criteria: implications for comparing effect sizes between trials.
abstract: BACKGROUND
  Comparing findings from separate trials is necessary to choose among treatment options, however differences among study cohorts may impede these comparisons.
  
  
  OBJECTIVE
  As a case study, to examine the overlap of study cohorts in two large randomized controlled clinical trials that assess interventions to reduce risk of major cardiovascular disease events in adults with type 2 diabetes in order to explore the feasibility of cross-trial comparisons
  
  
  METHODS
  The Action for Health in Diabetes (Look AHEAD) and The Action to Control Cardiovascular Risk in Diabetes (ACCORD) trials enrolled 5145 and 10,251 adults with type 2 diabetes, respectively. Look AHEAD assesses the efficacy of an intensive lifestyle intervention designed to produce weight loss; ACCORD tests pharmacological therapies for control of glycemia, hyperlipidemia, and hypertension. Incidence of major cardiovascular disease events is the primary outcome for both trials. A sample was constructed to include participants from each trial who appeared to meet eligibility criteria and be appropriate candidates for the other trial's interventions. Demographic characteristics, health status, and outcomes of members and nonmembers of this constructed sample were compared.
  
  
  RESULTS
  Nearly 80% of Look AHEAD participants were projected to be ineligible for ACCORD; ineligibility was primarily due to better glycemic control or no early history of cardiovascular disease. Approximately 30% of ACCORD participants were projected to be ineligible for Look AHEAD, often for reasons linked to poorer health. The characteristics of participants projected to be jointly eligible for both trials continued to reflect differences between trials according to factors likely linked to retention, adherence, and study outcomes.
  
  
  CONCLUSIONS
  Accurate ascertainment of cross-trial eligibility was hampered by differences between protocols.
  
  
  CONCLUSIONS
  Despite several similarities, the Look AHEAD and ACCORD cohorts represent distinct populations. Even within the subsets of participants who appear to be eligible and appropriate candidates for trials of both modes of intervention, differences remained. Direct comparisons of results from separate trials of lifestyle and pharmacologic interventions are compromised by marked differences in enrolled cohorts.
authors.affiliation: Wake Forest University School of Medicine, Winston-Salem, NC, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Mount
authors.forename: Patricia
authors.initials: P
authors.lastname: Feeney
authors.forename: Anthony N
authors.initials: AN
authors.lastname: Fabricatore
authors.forename: Mace
authors.initials: M
authors.lastname: Coday
authors.forename: Judy
authors.initials: J
authors.lastname: Bahnson
authors.forename: Robert
authors.initials: R
authors.lastname: Byington
authors.forename: Suzanne
authors.initials: S
authors.lastname: Phelan
authors.forename: Sharon
authors.initials: S
authors.lastname: Wilmoth
authors.forename: William C
authors.initials: WC
authors.lastname: Knowler
authors.forename: Irene
authors.initials: I
authors.lastname: Hramiak
authors.forename: Kwame
authors.initials: K
authors.lastname: Osei
authors.forename: Mary Ellen
authors.initials: ME
authors.lastname: Sweeney
authors.forename: Mark A
authors.initials: MA
authors.lastname: Espeland
mesh_terms: D000367:Age Factors; D001786:Blood Glucose; D001835:Body Weight; D002318:Cardiovascular Diseases / Q000209:etiology; D015331:Cohort Studies; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000188:drug therapy; D005006:Ethnicity; D005240:Feasibility Studies; D006801:Humans; D008019:Life Style; D008875:Middle Aged; D015337:Multicenter Studies as Topic; D018579:Patient Selection; D044469:Racial Groups; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012107:Research Design; D012307:Risk Factors; D012737:Sex Factors
chemical_list: D001786:Blood Glucose