[Quality of the information obtained by a questionnaire survey in studying the epidemiology of malignant neoplasms].

The quality of the data collected in a retrospective cohort breast cancer study in Estonia was evaluated. Two separate approaches were used to investigate possible biases in the study. Firstly, a similar questionnaire was mailed to a sample of 86 women twice during an interval of one week to six months. Overall questionnaire reliability was 83.4%. Secondly, comparisons of the data obtained by postal questionnaires about past history of lung tuberculosis with hospital medical record information revealed that 2.5% of women with severe forms of the disease and 30.3% with milder forms (controls) had denied their previous disease. These findings show that more attention must be paid to the quality control procedures in cancer epidemiology studies.