Repeatability of Self-reported Information for Population-based Studies of Cancer

Purpose: To measure the repeatability of a cancer risk factor questionnaire in a population-based case-controlstudy.
Methods: Questionnaires were completed on two occasions by patients with cancer of the ovary (n=25) oresophagus (n=23) and by 37 controls without cancer. We assessed general cancer risk factors including height andweight (for calculating body mass index (BMI)), smoking and anti-inflammatory (NSAID) use. Risk factors specificfor ovarian and esophageal cancers were also assessed. Agreement was measured by the correlation coefficient andweighted kappa statistic (kw) for continuous and categorical variables respectively.
Results: We observed very highlevels of agreement for BMI (kw=0.84) and smoking history, including ages at initiation and quitting (Pearsoncorrelation = 0.87 and 0.86 respectively). There was moderate to substantial agreement for use of anti-inflammatorydrugs (aspirin kw =0.52, other NSAIDS kw =0.72). Agreement for lifetime prevalence of medical conditions variedfrom almost perfect (e.g. history of benign breast disease (k =0.86)) to moderate (e.g. heartburn (k =0.57)). Itemrepeatability was not materially altered by case-control status, age or sex of respondents or interval betweencompletions.
Conclusions: Self-reported cancer risk factor information demonstrates moderate to almost perfectlevels of agreement, suggesting these items are suitable for risk estimation and epidemiologic inference.