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Suggested answer to exercise: Statins in pneumonia, 2

Question 2: What is meant by "P=0.15" and what can we conclude from it?

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Suggested answer

This is the result of a significance test, testing the null hypothesis that the
odds ratio in the population is one, i.e. that there is no difference
in the odds of an adverse outcome between patients on statins and patients
who were not on statins.

The P value is the probability of getting an odds ratio as far or further
from what we would expect as is the one we have observed,
if the null hypothesis were true.

As this P value is greater than 0.05, we would conclude that the data are not
consistent with the null hypothesis.
There is little or no evidence for us to conclude that the odds of a bad outcome
are different in patients on statins and patients not on statins.
Because P > 0.10, we do not even have very weak evidence.

Incidently, you may wonder why I keep asking the same questions about confidence
intervals and P values.
It is because I want you to become so familiar with these concepts that you don't
have to think about them!

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Last updated: 2 March, 2009.

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