Helping Doctors and Patients Make Sense of Health Statistics

1. Helping Doctors and Patients Make Sense of Health Statistics Supplemental Reading 2

2. Overview • Few understand health statistics • Mammography screening recues the risk of dying from breast cancer by 25% in fact means that _____________________will die of the disease. • Common to patients, journalists, and physicians • Created by nontransparent framing of information (sometimes intentional)

3. Have serious consequences • Not cognitive biases alone • Emotional nature of interaction • _____________________ • Potential solutions • Education (patients and physicians) • frequency statements vs. single event probabilities • _____________________ • mortality vs. survival rate • natural vs. conditional probabilities • Value of statistical literacy

4. Contraceptive pill scare • Finding = Oral contraceptive pills increased the risk of blood clots by _____________________ • Info passed on to 190,000 general practitioners • Caused anxiety, distressed women stopped taking pill

6. How big is 100% • Increased from _____________________people to 2/7000 people. • Absolute risk was only 1 in 7000, relative risk was 100% • Typically, • Absolute: _____________________ • Relative risk tend to look big esp. if base rate is low

7. Pill scare contributed to +13,000 abortions in the following year (+$76 million spent additionally) • For every + abortion, there was an additional birth, esp. in teenagers • +800 for girls under 16 • Abortions and pregnancies increased_____________________

8. Few gynecologists understand positive mammograms • Key stat: chances that a woman who tests positive actually has breast cancer • Mammograms produce many _____________________ • Women have the right to know • If you’re a woman who just received a positive screening mammogram, and asks your Dr.: • “Do I have breast cancer for certain, or what are the chances? 99%? 90% 50% or less?” • 160 gynecologists were provided information to make answer this question

10. Answer: _____________________(most Drs. Chose A or B; 21% got it right)

11. Conditional probabilities: includes sensitivity and the false-positive rate • _____________________: more transparent

14. After training, 89% got it right • Many physicians do no know the _____________________ that a person has a disease given a positive screening test

15. Higher survival does not mean longer life • Rudy Giuliani: • Britain: _____________________diagnosed with prostate cancer • 28 died within 5 years (~43%) • In US: 82% 5 year survival rate

16. 5 year survival rate • Key difference: _____________________ • Screening biases survival in 2 ways: • * affects timing of diagnosis (lead-team bias) • * affects the nature of diagnosis by including people with nonprogressive cancer (overdiagnosis bias)

17. Lead-time bias • Patients diagnosed with prostate cancer at 67 yr old, all die by 70 • Same group diagnosed at 60, all still die at 70 • 5 year survival rate is 100% but _____________________

18. Overdiagnosis bias • Detection of pseudodisease – meets pathologic definition but will never progress to cancer • _____________________

19. Changes in 5 year survival rate completely uncorrelated with changes in mortality • Knowing about changes in SURVIVAL tells you NOTHING about changes in MORTALITY • Giuliani wrong (WHY) • __________________________________________ • Real story is mortality rate • US: 26/100,000 die • Britain: 27/100,000 die

20. Examples Illustrate • Collective statistical literacy of patients, physicians, and politicians… • The more wide spread the literacy, the easier to manipulate

21. What is statistical literacy? • Basic competency in health statistic • Comparing survival rates with different screening policies: non-sense • Minimal statistical literacy in health

22. Minimal statistical literacy in health • Learning to live with uncertainty • There is no certainty and no zero-risk, but only risks that are more or less acceptable • Smoking vs. not smoking • BRCA1/2 • Bilateral mastectomy

23. Minimal statistical literacy in health • Questions to ask about all risks • Risk of what? (e.g., dying, getting disease, developing symptom) • Time frame? (10 years vs. life time) • How big? (expressed in _____________________–13/1000)

24. Minimal statistical literacy in health • Questions to ask about all risks (Cont.) • Does it apply to me? (age, sex, similar health problems) • Screening tests have benefits and harms • + finding disease earlier • - costs, inconvenience, false alarm, overdiagnosis—overtreatment • Detection  _____________________

25. Minimal statistical literacy in health • Screen tests can make two errors: • False positive (false alarm) • False negative (miss) • Understand how to translate probabilities into natural frequencies • Study: undercover at 20 AIDS counselors: “If one is not infected with HIV, is it possible to have a positive test result?”

26. Minimal statistical literacy in health • Understand that the goal of screening is not to simply the early detection of d_____________________disease; it is mortality reduction or improvement of quality of life.

27. Minimal statistical literacy in health • Treatments have benefits and harms • More is not always better • Understand the size of the benefit and harm • Ask for _____________________ (not relative) of outcomes w/ and w/out treatment • Questions about the science behind the numbers (e.g., quality of study) • What conflicts of interest exist?

28. Prevalence of health statistical illiteracy

29. Consequences • Susceptibility to manipulations of anxieties and hopes • Informed consent and shared decision making undermined

34. Causes of health illiteracy • Paternalism and trust • Determinism and illusion of certainty • Conflicts of interest

35. Potential solutions • Teach statistical literacy in school • Too late in school • With representations that confuse young minds • Boring examples that kill motivation • Teachers who are unversed in statistics • Transparency • Numbers, not only words • Data tables: Drug fact boxes • Transparent numbers