Since this was a pilot study, the main question of interest is how many subjects would be needed to detect an increase of 10 g in mean LVM over 4 years using a twosided test with α = 0.05 and power = 80%? 

Cardiovascular Disease, Pediatrics

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 change in LVM between the 2 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 4 years of follow-up. The data are given in Table 7.6.

Table 7.6: Pilot data on left ventricular mass (LVM) in children from the Bogalusa Heart Study

 

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Change (g)* ID Baseline LVM (g) 4-year LVM (g) 139 163 24 134 126 -8 86 142 56 4 98 96 -2 78 111 33 90 108 18 7 102 167 65 73 8. 82 93 77 -16 10 162 172 10 Mean 105.5 124.4 18.9 sd 29.4 35.2 26.4 *4-year LVM minus baseline LVM