Self-reported information on the diagnosis of colorectal cancer was reliable but not necessarily valid

Self-report is commonly used in epidemiologic studies; however, few data exist on the reliability and validity of this method for eliciting information related to the diagnosis of colorectal cancer. We examined the test-retest reliability and validity of colorectal cancer patients reporting on the process of their diagnosis.

One hundred and sixteen participants completed two telephone interviews, 1 month apart, and 95 general practitioners (GPs) completed a written questionnaire, to elicit information relating to key elements of the process of diagnosis of colorectal cancer.

Acute symptoms such as rectal bleeding had higher reliability and validity than more general symptoms. Colonoscopy was the most accurately recalled diagnostic test. Recall of diagnosis date, and date of colonoscopy, had high test-retest reliability. There were considerable differences between dates of diagnostic tests given by participants and GPs, but there was no evidence of a bias in a particular direction. Accuracy of recall did not diminish as time from diagnosis increased.

This study confirms that self-reported symptoms, tests, and dates in the colorectal cancer diagnostic pathway are generally reliable; however, the validity of reported symptoms and tests can be moderate to poor.