**Nicotine replacement does help**

This is an example of a meta-analysis of many studies to give an overall result for smokers who use one of several forms of nicotine replacement. This is a complex procedure which could itself be a subject for further investigation by advanced students. However the interpretation of the claim of smokers using the therapy being 1.7 times more likely to kick the habit leads to the question, "More likely than who?" What is not clear is what the conditions are under which the probabilities were calculated. For example it might be inferred from the statement that

Pr (give up smoking | nicotine treatment) = 1.7 Pr (give up smoking | no treatment)

[Here Pr (A | B) is the probability of event A occurring given the occurrence of event B].

If this were in fact the appropriate interpretation, how significant is it in relation to the costs of such programs?

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