[Indicating risks in the Dutch Cancer Society Cancer Risk Test: indicating population risks improves risk perception]

To have the Dutch Cancer Society Cancer Risk Test (KWF-KRT) assessed by users and to determine the effect of the numerical indication of risks on the perception of cancer risks.

Cross-sectional questionnaire study.

In total 612 persons from the general population were given a shortened test version of the KWF-KRT test for colon and lung cancer via the Internet. 12 different versions were tested, differing in the quantification of risks. Each participant received one version of the test for colon cancer and one for lung cancer. Before and after taking the KWF-KRT, participants were asked to complete a questionnaire.

Completing the KWF-KRT version without numbers improved the understanding of the relative risk of colon cancer. Beforehand, 57% of the participants underestimated their personal cancer risk for colon cancer and 38% their risk for lung cancer. Addition of quantitative information on the population risk to the standard test resulted in twice as many correct estimates of the population risk and significantly improved the estimates of personal risk. It made no difference whether the population risk was presented only in numbers or also as a population diagram. The quantification of the personal risk and risk reduction had no effect. Approximately 12% of the participants indicated that they had become more worried about the risk of cancer after completing the test. The assessment of the KWF-KRT by the participants was largely positive.

Adding quantitative information about the population risk led to a better understanding of both the population risk and the personal risk of cancer.