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.