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Power vs. the risk difference 
for different cluster random
effect distributions, with baseline risk 
, number of
steps 
, number of clusters
, and cluster size
. For figures in the left column,
; while for figures in the
right column, 
. There are no time effects
(
) in the first row, very small
time effects (
) in the second row, and
moderate time effects (
) in the third row.
