Left ventricular mass (LVM) is an important risk factor for subsequent cardiovascular disease. A study is proposed to assess the relationship be- tween 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 ele- vated 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 1 ID Baseline LVM (g) 1 139 2 134 3 86 4-year LVM (g) 163 126 142 Change (g) 24 -8 56 4 98 96 -2 5 78 6 90 7 102 8 73 82 9 9 93 77 -16 10 162 Mean 105.5 172 10 124.4 18.9 35.2 26.4 sd 29.4 Table 1: Pilot data on left ventricular mass (a) What test can be used to assess if there is a change in mean LVM over 4 years? (b) Implement the test in (a) and provide a two-tailed p-value. (c) Provide a 95% CI for the change in LVM over 4 years. (d) 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%? Hint: Assume that the estimated variance of change in LVM in the pilot study is the true variance of change in LVM.
Left ventricular mass (LVM) is an important risk factor for subsequent cardiovascular disease. A study is proposed to assess the relationship be- tween 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 ele- vated 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 1
ID Baseline LVM (g) 1 139
2 134
3 86
4-year LVM (g) 163
126
142
Change (g) 24
-8
56
4 98 96 -2
5 78
6 90
7 102
8 73 82 9 9 93 77 -16
10 162 Mean 105.5
172 10 124.4 18.9 35.2 26.4
sd 29.4
Table 1: Pilot data on left ventricular mass
-
(a) What test can be used to assess if there is a change in mean LVM over 4 years?
-
(b) Implement the test in (a) and provide a two-tailed p-value.
-
(c) Provide a 95% CI for the change in LVM over 4 years.
-
(d) 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%? Hint: Assume that the estimated variance of change in LVM in the pilot study is the true variance of change in LVM.
Trending now
This is a popular solution!
Step by step
Solved in 3 steps
