How do you handle probabilistic knowledge?

[Ivor the Engineer]

http://en.wikipedia.org/wiki/Cultural_Theory_of_risk

So which best describes you: Individualist, Egalitarian, Hierarchist, Fatalist or Autonomous?

Personally, I think I'm pretty evenly spread between Egalitarian Individualist and Hierarchist. I blame my parents.

 

[Ivor the Engineer]

Here's a couple of pages which describe how we struggle to comprehend probabilistic information and gives some examples of ways of presenting it which may make such information easier or more difficult to grasp.

http://www.medicine.ox.ac.uk/bandolier/band128/b128-6.html

Study

The setting was 120 adult patients attending a cardiac rehabilitation clinic after bypass surgery or myocardial infarction, and taking simvastatin or atorvastatin. The only exclusions were inability to read or where first language was not English.

There were two variables. Two different adverse events of statins were chosen, constipation and pancreatitis, and the adverse event information was presented using words or numbers (Presentation Box below), using EU guidelines (Table 1). Half of the participants received information about constipation, and the other half information about pancreatitis (atorvastatin users only). Within each group, half received the information using words, and half using numbers. Allocation was random.


Results

The age range of participants was 35 to 74 years (median 63), and they had been taking a statin for one to 70 months (median six). The majority (56%) had no formal educational qualifications.

For both constipation and pancreatitis, participants overestimated the percentage chance of the adverse event affecting them (Figure 1). The degree of overestimation was far higher using words than using numbers. Using words rather than numbers also increased patient estimates of the event happening to them using a six point scale, with small differences in some other questions, and satisfaction with information presented was somewhat higher with numbers than with words.

http://www.medicine.ox.ac.uk/bandolier/band144/b144-3.html

Risk perception and presentation

A study [1] was carried out on two groups, 38 graduate students and 47 healthcare professionals. A hypothetical situation about adverse events of an influenza vaccine was presented to them in either a probability format (5%), or a frequency format (1 in 20). Randomisation was by alternation in questionnaire handouts.

The questionnaire asked whether they would be prepared to receive a vaccine if the risk of fever and headache within seven days was either 5% (one group) or 1 in 20 (the other). A second question asked participants to match frequency with one of six phrases, from very common to very rare.


Results

There was no difference between occupation, age, or sex of the groups receiving information as probability or frequency. About 60% of participants would have elected to have the influenza vaccine, without any significant difference between a probability format (67% electing to receive it) and the frequency format (55%).

There were differences between the way in which the risk was matched to phrases (Figure 1). In both presentations, the same risk was labelled as very common, through to rare. Presentation as frequency (1 in 20) resulted in much greater consensus, with 84% happy that this could be called common or occasional, and only 9% considering it either rare or very common.