title: The impact of survey nonresponse bias on conclusions drawn from a mammography intervention trial.
abstract: OBJECTIVE
  This study demonstrates the impact of survey nonresponse bias on conclusions from a mammography trial targeting a disadvantaged population.
  
  
  METHODS
  The trial randomized 1558 women to three interventions designed to promote repeat mammography: mailed reminder (minimum group); mailed thank-you card, patient newsletters, and reminder (maximum group); and no mailings (control group). The primary outcome, repeat mammogram within 15 months, was assessed from administrative and phone survey data.
  
  
  RESULTS
  Administrative estimates revealed a statistically significant difference of 7% between the maximum and control groups on the primary outcome. Survey estimates (response rate 80%) revealed no significant differences. The differences by data source were traced to a survey nonresponse bias. There was a statistically significant difference of 16% between the maximum and control groups among survey nonrespondents for the primary outcome, but there were no differences among survey respondents.
  
  
  CONCLUSIONS
  The findings reiterate that even a low survey nonresponse rate can bias study conclusions and suggest studies targeting disadvantaged populations should avoid relying solely on survey data for outcome analyses.
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000517:prevention & control; D003627:Data Interpretation, Statistical; D005260:Female; D006306:Health Surveys; D006801:Humans; D008327:Mammography; D008875:Middle Aged; D011203:Poverty; D015983:Selection Bias; D016312:Treatment Refusal