title: Role of survivor bias in pancreatic cancer case-control studies.
abstract: OBJECTIVE
  The purpose of this study was to evaluate the impact of survivor bias on pancreatic cancer case-control studies.
  
  
  METHODS
  The authors constructed five case-loss scenarios based on the Iowa Women's Health Study cohort to reflect how case recruitment in population-based studies varies by case survival time. Risk factors for disease incidence included smoking, body mass index (BMI), waist circumference, diabetes, and alcohol consumption. Odds ratios (ORs) were estimated by conditional logistic regression and quantitatively compared by the interactions between risk factors and 3-month survival time. Additionally, Kaplan-Meier estimates for overall survival were compared within the subset cohort of pancreatic cancer cases.
  
  
  RESULTS
  BMI and waist circumference showed a significant inverse relationship with survival time. Decreasing trends in ORs for BMI and waist circumference were observed with increasing case survival time. The interaction between BMI and survival time based on a cutpoint of 3 months was significant (P < .01) as was the interaction between waist circumference and survival time (P < .01).
  
  
  CONCLUSIONS
  The findings suggested that case losses could result in survivor bias causing underestimated odds ratios for both BMI and waist circumference, whereas other risk factors were not significantly affected by case losses.
authors.affiliation: Center for International Blood and Marrow Transplant Research, Department of Medicine, Medical College of Wisconsin, Milwaukee. Electronic address: zhu@mcw.edu.
authors.forename: Zhen-Huan
authors.initials: ZH
authors.lastname: Hu
authors.affiliation: Division of Biostatistics, School of Public Health, University of Minnesota, Minneapolis.
authors.forename: John E
authors.initials: JE
authors.lastname: Connett
authors.affiliation: University of Pittsburgh Cancer Institute and Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA.
authors.forename: Jian-Min
authors.initials: JM
authors.lastname: Yuan
authors.affiliation: Division of Epidemiology & Community Health, School of Public Health, University of Minnesota, Minneapolis.
authors.forename: Kristin E
authors.initials: KE
authors.lastname: Anderson
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D016022:Case-Control Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007484:Iowa / Q000453:epidemiology; D053208:Kaplan-Meier Estimate; D016015:Logistic Models; D008875:Middle Aged; D016017:Odds Ratio; D010190:Pancreatic Neoplasms / Q000453:epidemiology* / Q000209:etiology / Q000401:mortality; D011446:Prospective Studies; D012307:Risk Factors; D015983:Selection Bias; D017741:Survivors; D013997:Time Factors; D055105:Waist Circumference
keywords: Body mass index; Case control study; Pancreatic neoplasm; Survivor bias; Waist circumference