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 (< 90th="" 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="" two="" groups.="" before="" this="" can="" be="" done,="" one="" needs="" to="" demonstrate="" that="" lvm="" actually="" changes="" in="" children="" over="" a="" 4-year="">
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 .
Table 1 Pilot data on left ventricular mass (LVM) in children from the Bogalusa Heart Study
ID |
Baseline LVM (g) |
4- year LVM (g) |
Change (g)* |
1 |
139 |
163 |
24 |
2 |
134 |
126 |
-8 |
3 |
86 |
142 |
56 |
4 |
98 |
96 |
-2 |
5 |
78 |
111 |
33 |
6 |
90 |
108 |
18 |
7 |
102 |
167 |
65 |
8 |
73 |
82 |
9 |
9 |
93 |
77 |
-16 |
1: Suppose the investigators are reluctant to assume that the change in LVM over four years is normally distributed. What test can be used to assess if there is a change in mean LVM over four years?
Wilcoxon Rank-Sum test can be used or not?
2 : What are the hypotheses being tested with this test?
3 :Despite the n = 10, assume that the large sample method of significance testing is valid for these data and perform the test by hand. Make a conclusion based on 5% significance level using p-value. Show details of work.