Since this was a pilot study, the main question of interest is how many subjects would be needed to detect a mean increase of 10 g in LVM over four years using a two-sided test with a = 0.05 and power = 80%?

Cardiovascular Disease

Left ventricular mass (LVM) is an important risk factor for subsequent cardiovascular disease. A study is proposed to assess the relationship between childhood blood-pressure levels and LVM in children as determined from echocardiograms. The goal is to stratify children into a normal bp group (< 80th percentile for their age, gender, and height) and an elevated bp group (‰¥ 90th percentile for their age, gender, and height) and compare the change in LVM between the two groups. 

Before this can be done, one needs to demonstrate that LVM actually changes in children over a 4-year period.

To help plan the main study, a pilot study is conducted where echocardiograms are obtained from 10 random children from the Bogalusa Heart Study at baseline and after four years of follow-up (Urbina et al., Personal Communication). The data are given in Table 8.27.

Table 8.27: Pilot data on left ventricular mass (LVM) in children from the Bogalusa Heart Study

 

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Baseline LVM (g) ID 4-year LVM (g) Change (g)* 1 139 163 24 134 126 -8 86 142 56 4 98 96 -2 78 111 33 90 108 18 102 167 65 73 82 93 77 -16 10 162 172 10 Mean 105.5 124.4 18.9 sd 35.2 29.4 26.4 *4-year LVM minus baseline LVM