>  If some, but not all, of the colonies were treated with coumaphos
>before the test was the data checked for an impact of the treated vs
>non-treated on the results of the study?

You should read what I said more carefully. Two whole  apiaries were
treated and two were not. Screens were used on half of the hives in
each apiary. Treated hives had low mites overall and untreated hives
had high mites overall. Screens had no significant effect.

>This would be an added variable in the experiment that would at
>least need to be accounted for.

Coumaphos was not a variable and did not skew the data within the
apiary where it was used nor where it was not used.

>This along with the relatively small numbers of colonies reported
>could explain the inability of the study to detect any effect on
>varroa mite populations in the test colonies.

60+ hives is a small number? A study like this cost thousands of
dollars and to my knowledge, no one else has done one like it. The
inability to detect effect is due to the fact that the screens did
not reduce mites. Other researchers have told me that they now agree
that screens alone are not effective. Some claim they are effective
when combined with chemicals. The study in ABJ describes this theory
though if you read the fine print, they  found increased numbers of
mites on the bottom board combining screens with chemicals, but the
load on the bees seemed to be not affected.

>Open bottoms have other positive features as many have pointed out
>but their impact on varroa at a practical level, used alone, is not
>enough to help.  The colonies will still die.

Our study showed no difference in honey production, or fall cluster
size. In order to consider a tool an IPM technique, it has to work.
Otherwise, it's just faith healing.

>One who has all his colonies on mesh bottoms and thinks the bees "like it"

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