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Exercise: Comparing means, 6

Question 6. Is there anything to suggest that the t test may not be valid?

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Suggested answer

It is not likely that semen count follows a Normal distribution.
The standard deviation is more than half the mean,
so mean minus 2 SD would be negative.
We would expect 2.5% of observations to be below this if the distribution were Normal.
This would imply negative values, which would be impossible.

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Last updated: 27 July, 2009.

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