period x sequence [Design Issues]

posted by d_labes  – Berlin, Germany, 2016-12-21 11:45 (2546 d 05:46 ago) – Posting: # 16869
Views: 8,121

Dear ElMaestro,

❝ ❝ 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.

Regards,

Detlew

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