period x sequence [Design Issues]
❝ ❝ Is it possible to determine the interaction between period and sequence effect?
❝ Yes. It is a treatment effect.
❝ E.g. Period 1 in (or x) Sequence TR is effectively just treatment T (in that period). Note that some serious DF elimination may come into play depending on how you specify the model. For example, in the model matrix the columns for "period 1 in Seq TR" and "period 2 in Seq RT" will add up to exactly the column for the Treatment T effect. If you have the interaction before the treatment in your model spec, then the latter will get a type I SS and MS of zero.
IMHO your description is totally correct.
But my judgment to Johns question would be different:
No. Its not possible to to determine the interaction between period and sequence effect and the treatment effect in a classical 2x2 crossover. Both terms are confounded.
It's the same situation if you try to determine a carry-over effect and a direct sequence effect simultaneously.
- Significant period effect jag009 2016-12-20 04:48 [Design Issues]