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

Abstract

Purpose: To measure the repeatability of a cancer risk factor questionnaire in a population-based case-controlstudy. <br/><b>Methods</b>: 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. <br/><b>Results</b>: 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. <br/><b>Conclusions</b>: Self-reported cancer risk factor information demonstrates moderate to almost perfectlevels of agreement, suggesting these items are suitable for risk estimation and epidemiologic inference.