Repeatability of self-reported information for population-based studies of cancer

To measure the repeatability of a cancer risk factor questionnaire in a population-based case-control study.

Questionnaires were completed on two occasions by patients with cancer of the ovary (n=25) or esophagus (n=23) and by 37 controls without cancer. We assessed general cancer risk factors including height and weight (for calculating body mass index (BMI)), smoking and anti-inflammatory (NSAID) use. Risk factors specific for ovarian and esophageal cancers were also assessed. Agreement was measured by the correlation coefficient and weighted kappa statistic (kw) for continuous and categorical variables respectively.

We observed very high levels of agreement for BMI (kw=0.84) and smoking history, including ages at initiation and quitting (Pearson correlation = 0.87 and 0.86 respectively). There was moderate to substantial agreement for use of anti-inflammatory drugs (aspirin kw =0.52, other NSAIDS kw =0.72). Agreement for lifetime prevalence of medical conditions varied from almost perfect (e.g. history of benign breast disease (k =0.86)) to moderate (e.g. heartburn (k =0.57)). Item repeatability was not materially altered by case-control status, age or sex of respondents or interval between completions.

Self-reported cancer risk factor information demonstrates moderate to almost perfect levels of agreement, suggesting these items are suitable for risk estimation and epidemiologic inference.