Exercise: Comparing means, 6

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

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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