Suggested answer to exercise: Evaluation of a nurse-run asthma school, 3

Question 3: What limitations does the lack of a control group lead to?

Suggested answer

We cannot say whether any changes which took place over the year would have taken place anyway, without the Asthma School. Patients will be exposed to many other influences apart from the School.

The fact that a difference is significant means only that a change would have taken place in the population, not that is was caused by any particular intervention.

A randomised control group, comparable apart from the Asthma School, would enable us to conclude that any differences were the effect of the Asthma School.

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Last updated: 20 October, 2006.

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