The linearity of the effects of sodium within the control diet or
the DASH diet was assessed by comparing the decrease in blood
pressure from the high to the intermediate level of sodium with the
decrease from the intermediate to the low level of sodium. Multiple
comparisons were accounted for by means of the method of Holmthe resulting adjusted P values could be compared to 0.05 to determine
significance.
20
The adjusted P values were used for the bloodpressure
changes in the total cohort, but not in subgroups, as specified
in the study protocol. All analyses were performed according
to the intention-to-treat approach; in 22 instances, missing bloodpressure
measurements during an intervention period, including
those owing to a participant’s withdrawal from the study, were replaced
by base-line values. The planned sample size of 400 was calculated
in order to provide the study with a power of 90 percent
to detect a difference in systolic blood pressure of 2.1 mm Hg between
sodium levels, and a difference of 3.0 mm Hg between the
DASH and control diets at each sodium level.