The data in the table are a sample of cholesterol levels taken from 24 hospital employees who were on a standard American diet and who agreed to adopt a vegetarian diet for 1 month. Serum-cholesterol measurements were made before adopting the diet and 1 month after.
TABLE Serum-cholesterol levels (mg/dL) before and after adopting a vegetarian diet
SUBJECT BEFORE AFTER DIFFERENCE
1 137 125 12
2 178 137 41
3 161 153 8
4 167 154 13
5 168 145 23
6 168 176 -8
7 222 187 35
8 180 161 19
9 197 178 19
10 151 149 2
11 158 127 31
12 169 182 -13
13 197 169 28
14 238 206 32
15 224 208 16
16 192 184 8
17 236 215 21
18 250 202 48
19 166 147 19
20 244 208 36
21 159 146 13
22 205 178 27
23 145 155 -10
24 195 146 49
1. Compute the average or mean change in cholesterol levels.
2. Compute the standard deviation of the change in cholesterol levels.
3. Compute the median change in cholesterol.
4. Construct a box plot of the cholesterol changes to the right.
5. Comment on the symmetry of the distribution of change scores based on your answers to Problems 1 and 4.
6. Some investigators believe that the effects of diet on cholesterol are more evident in people with high rather than low cholesterol levels. If you split the data in the table according to whether baseline cholesterol is above or below the median, can you comment descriptively on this issue?