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33) Screening Tests Understand that screening tests may have benefits and harms. The two shaded areas indicate the two possible errors, false positives and false negatives (data adopted from Snijders, Noble, Sebire, Souka, & Nicolaides, 1998). Overdiagnosis can be defined as the detection of pseudodisease or abnormalities that would never progress to cause symptoms in the patient’s lifetime. , 2001). The treatment of nonprogressive cancers results in unnecessary surgery and other invasive treatments—treatments that can only harm patients since they are being treated for a “disease” that would never have harmed them if left untreated.

What is your best guess about how many times the coin would come up heads in 1,000 flips? 1% 25 23 21 30 27 How many heads in 1,000 76 coin flips? Lipkus, Samsa, and Rimer (2001) even found that only 21% of well-educated adults could answer this question correctly. 5: Proportion of Correct, Incorrect, and Missing Answers to the 18 Items on the Medical Data Interpretation Test for 178 Participants Answered Correctly (%) Answered Incorrectly (%) Left Blank (%) Know that a denominator is needed to calculate risk 75 24 1 Know that denominators are needed to compare risks in 2 groups 45 54 1 Know that the base rate is needed in addition to relative risk to determine the magnitude of benefit 63 36 1 Knowledge Basis for Comparisons Page 9 of 39 Helping Doctors and Patients Make Sense of Health Statistics Know that a comparison group is needed to decide whether benefit exists 81 18 1 Know that lowering all-cause mortality provides better evidence of benefit than lowering a single cause of death 20 79 1 85 14 1 Rate the riskiness of a 9 in 1,000 chance of death as the same as a 991 in 1,000 chance of surviving 61 37 2 Select a larger risk estimate for deaths from all causes than deaths from a specific disease 30 69 1 Select a larger risk estimate for a 20-year risk than for a 10-year risk 39 60 1 Calculate risk in intervention group by applying relative risk reduction to a baseline risk 87 11 2 Calculate 2 absolute risk reductions from relative risk reductions and baseline risks and select the larger 80 19 1 Calculate relative risk reduction from 2 absolute risks 52 46 2 Calculate absolute risk reduction from 2 absolute risks 77 19 4 Calculate the number of events by applying absolute risk to number in group 72 22 6 Comparison Tasks Select “1 in 296” as a larger risk than “1 in 407” Inferred Itemsa Calculations Related to Comparisons Context for Comparisons Know that age and sex of individuals in the source data are needed 47 51 2 Know that age of individuals in the source data is needed 60 39 1 Know that risk of other diseases is needed for context 62 35 3 Know that, for male smokers, the risk of lung cancer death is greater than prostate cancer death 60 37 3 (a ) These items were based on a total of 5 separate questions.

586). This awkward statement is a hybrid between a single-event probability (it is about “you”) and a frequency statement yet is not an absolute risk reduction (Gigerenzer, 2003). A review of experimental studies showed that many patients do not understand the difference between relative and absolute risk reduction and that they evaluate a treatment alternative more favorably if benefits are expressed in terms of relative risk reduction (Covey, 2007). This lack of basic health literacy prevents patients from giving informed consent.