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Suggested answer to exercise: Nurse delivered home exercise programme, 1

Question 1: The 'mean (SD)' of the number of current prescribed drugs were
3.1 (2.4) and 2.9 (2.3) for the two groups.
What does this mean?
What does it tell us about the shape of the distribution of the number of prescribed drugs taken?

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Suggested answer

Each patient reported a number of prescribed drugs, 0, 1, 2, 3, etc.
The average of these numbers is the mean.
The SD is the standard deviation, which measures how variable these numbers of drugs are.
About 2/3 of the drug numbers will lie within one SD of the mean, about 95% within 2 SD.

As the SD is almost as large as the mean, mean - 2SD will be negative.
If the distribution were symmetrical (or negatively skew),
this would imply some negative observations.
Number of drugs cannot be negative, so the distribution must be
positively skew or skew to the right.

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Last updated: 6 November, 2006.

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