Exercise: breast pump trial, 2
Question
What effect might each of these problems have on the t test?
Suggested answer

Treating repeated observations by the same method as independent gives us a false idea
of the amount of information.
This makes P values smaller than they should be.

Carrying out a two sample t test on paired data means that all the variation between women
goes into the random variation.
This tends to make the P value too large.

Carrying out a test when variances are unequal and distributions skew may make the P value too large.
Back to question.
Back to IAPT index.
To Martin Bland's home page.
This page maintained by Martin Bland.
Last updated: 27 February, 2009.
Back to top.