The Barrier to Informed Choice in Cancer Screening: Statistical Illiteracy in Physicians and Patients

Abstract

An efficient health care requires both informed doctors and patients. Our current healthcare system falls short on both counts. Most doctors and patients do not understand the available medical evidence. To illustrate the extent of the problem in the setting of cancer screening: In a representative sample of some 5000 women in nine European countries, 92% overestimated the reduction of breast cancer mortality by mammography by a factor of 10-200, or did not know. For a similar sample of about 5000 men with respect to PSA screening, this number was 89%. Of more than 300 US citizens who regularly attended one or more cancer screening test, more than 90% had never been informed about the biggest harms of screening-overdiagnosis and overtreatment-by their physicians. Among 160 German gynecologists, some 80% did not understand the positive predictive value of a positive mammogram, with estimates varying between 1 and 90%. In a national sample of 412 US primary care physicians, 47% mistakenly believed that if more cancers are detected by a screening test, this proves that the test saves lives, and 76% wrongly thought that if screen-detected cancers have better 5-year survival rates than cancers detected by symptoms, this would prove that the screening test saves lives. And of 20 German gynecologists, not a single one provided a woman with all information on the benefits and harms of cancer screening required in order to make an informed choice. Why is risk literacy so scarce in health care? One frequently discussed explanation assumes that people suffer from cognitive deficits that make them predictably irrational and basically hopeless at dealing with risks, so that they need to be "nudged" into healthy behavior. Yet research has demonstrated that the problem lies less in stable cognitive deficits than in how information is presented to physicians and patients. This includes biased reporting in medical journals, brochures, and the media that uses relative risks and other misleading statistics, motivated by conflicts of interest and defensive medicine that do not promote informed physicians and patients. What can be done? Every medical school should teach its students how to understand evidence in general and health statistics in particular. To cultivate informed patients, elementary and high schools should start teaching the mathematics of uncertainty-statistical thinking. Guidelines about complete and transparent reporting in journals, brochures, and the media need to be better enforced, and laws need to be changed in order to protect patients and doctors alike against the practice of defensive medicine instead of encouraging it. A critical mass of informed citizens will not resolve all healthcare problems, but it can constitute a major triggering factor for better care.

Keywords: 5-year survival; Absolute risk; Cancer screening; Informed decision-making; Medical risk communication; Medical risk illiteracy; Relative risk.