1. Risk Perception and Communication
The risks that upset people are completely different
than the risks that kill people. Peter Sandman
Risk Perception and Communication
Wolfgang Gaissmaier, PhD
Department of Psychology
Social Psychology and Decision Sciences

2. Misperception of risk
Statistical information is notoriously difficult to understand
Gigerenzer, Gaissmaier, et al (2007). Psychological Science in the Public Interest
People fear the wrong things: Flying ↑, Disease progression of MS↓, cardiovascular disease↓ Gaissmaier & Gigerenzer (2012). Psychological Science Heesen, Gaissmaier, et al (2013). PLoS One Oertelt-Prigione, Seeland, Kendel, Rücke, Flöel, Gaissmaier, et al (2015). BMC Medicine Slovic (1987). Science
They overestimate the benefits of medical treatments Gigerenzer, Mata, & Frank (2009). JNCI Heesen, Kleiter, Nguyen, Schäffler, Kasper, Köpke, & Gaissmaier (2010). Multiple Sclerosis

3. 3

4. Ecological Rationality
Mind
Environment
Gigerenzer & Gaissmaier (2011). Annual Review of Psychology

5. 160 Gynecologists estimate: Probability of breast cancer | positive mammogram
Estimates (%)
Beste Schätzung
Before Training
Gigerenzer, Gaissmaier, Kurz-Milcke, Schwartz & Woloshin (2007). Psychological Science in the Public Interest

6. ~10 % Mammography 10 cancer 990 no cancer 9 positive 89 1 negative 901
1000
women
Natural Frequencies
Conditional Probabilities
p(breast cancer) = 1%
p(positive|cancer) = 90%
p(positive|no cancer) = 9%
.01 x .90
.01 x x .09
p(cancer|positive) =
p(cancer|positive) = 9
9 + 89
~10 %
Mammography

7. 160 Gynecologists estimate: Probability of breast cancer | positive mammogram
Estimates (%)
Best Estimate
Before Training
After Training
Gigerenzer, Gaissmaier, Kurz-Milcke, Schwartz & Woloshin (2007). Psychological Science in the Public Interest

8. “I had prostate cancer, five, six years ago
“I had prostate cancer, five, six years ago. My chances of surviving prostate cancer, and thank God I was cured of it, in the United States, 82 percent. My chances of surviving prostate cancer in England, only 44 percent under socialized medicine.”
Rudy Giuliani
New Hampshire radio advertisement, October 29, 2007

9. Lead time bias 9

10. Overdiagnosis bias 10

11. Wegwarth, Gaissmaier, & Gigerenzer (2010). Medical Decision Making
2 in 1,000 vs.
1.6 in 1,000
68% vs. 99%
Wegwarth, Schwartz, Woloshin, Gaissmaier, & Gigerenzer (2012). Annals of Internal Medicine
Wegwarth, Gaissmaier, & Gigerenzer (2010). Medical Decision Making

12. Facts boxes Simple tabular representation
Balanced overview of benefits and harms
Reducing the information to the most relevant pieces
Simulatneous comparison between people
with different treatments
with treament vs. placebo
(pre- vs. post-treatment)
Are very well accepted by patients
Facilitate comprehension as well as the identification of superior options
Schwartz, Woloshin, & Welch (2007) Medical Decision Making
Schwartz, Woloshin, & Welch (2009) Annals of Internal Medicine

13. Prostate Cancer Early Detection by PSA screening and digital-rectal examination. Numbers are for men aged 50 years or older, not participating vs. participating in screening for 13 years.
Benefits
1,000 men
without
screening
with
How many men died from prostate cancer? 5* 4
How many men died from any cause?
Harms
How many men were diagnosed and treated** for prostate cancer unnecessarily? – 30
How many men without cancer got a false alarm and a biopsy?
170
* This means that about 5 out of 1,000 men (50+ years of age) without screening died from prostate cancer within 13 years.
** With prostate removal or radiation therapy, which can lead to incontinence or impotence.
Source: Schröder FH, Hugosson J, Roobol MJ, et al. (2014). The Lancet.

14. Graphical representations
help people digest numbers
are preferred
reduce the influence of biases such as the ones presented earlier (framing, anecdotes, etc.)
support healthy behaviors
Gaissmaier et al. (2012) Health Psychology
Garcia-Retamero & Cokely (2013) Current Directions in Psychological Science
Trevena et al. (2013) BMC Medical Informatics and Decision Making

15. Prostate Cancer Early Detection by PSA screening and digital-rectal examination. Numbers are for men aged 50 years or older, not participating vs. participating in screening for 10 years.
1,000 men without screening:
1,000 men with screening: P P P P P P P P P X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X
Men dying from prostate cancer:
Men dying from any cause:
Men that were diagnosed and treated for prostate cancer unnecessarily:
Men without cancer that got a false alarm and a biopsy:
Remaining men 5
200 – 4
200 30
170 P X
Source:
Schröder FH, Hugosson J, Roobol MJ, et al. (2014). The Lancet.

16. Conclusions Clinical evidence is notoriously difficult to understand
Statistics are an educational blind spot of many people
Transparent representations foster insight
But: Behavior does not really change
Gaissmaier & Gigernzer (2011). Better Doctors, Better Patients, Better Decisions.

17. Conclusions Lack of evidence culture
Ideologies often matter more than evidence
How can evidence be made not only understandable, but convincing?
Social heuristics: Trust in authorities (e.g., physicians)
Authorities may lack understanding
Conflicts of interest
Defensive decision making
When do social heuristics make sense?
Gaissmaier & Gigernzer (2011). Better Doctors, Better Patients, Better Decisions.