Question
A study was conducted to investigate how effective a new diet was in lowering cholesterol. Results for the randomly selected subjects are shown in the table. The differences have a normal distribution. Are the subjects’ cholesterol levels lower on average after the diet? Test at the 5% level.
Table 10.13: Before-and-after cholesterol by subject
| Subject | A | B | C | D | E | F | G | H | I |
|---|---|---|---|---|---|---|---|---|---|
| Before | 209 | 210 | 205 | 198 | 216 | 217 | 238 | 240 | 222 |
| After | 199 | 207 | 189 | 209 | 217 | 202 | 211 | 223 | 201 |
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Evidence boundary
This answer uses Try It 10.11, Table 10.13 in the 2013 OpenStax PDF, preserving all nine subject pairs and the stated normality assumption. Different subjects’ differences are treated as independent. Units are not supplied. Calculations are independently recomputed; the before-and-after result is not proof that the diet alone caused the change and is not medical advice.