EXPERIMENTAL AND QUASI-EXPERIMENTAL STUDY DESIGNS
(TAKEN FROM CAMPBELL & STANLEY)
Beware of the simple two-point result, especially the tendency to
imagine a clear 'improvent' between them
In this model, there seems to be no effect measureable apart from the
Similarly here: the intervention appears to be ineffective
Here again, the 'jump' has been lost in the background 'noise'
This could be a real effect and should be studied further
This could be a delayed effect. Worth further study
The advantages of the cross-over trial are that fewer numbers
are needed because ALL people are exposed at different times
to BOTH arms of the study. Also, the "order" effect can be studied.
But it demands a full "washout" period to be sure that no residual
remains. Full double-blinding is essential.