Question 1082861: When subjects were treated with a drug, their systolic blood pressure readings (in mm Hg) were measured before and after the drug was taken. Results are given in the table below. Assume that the paired sample data is a simple random sample and that the differences have a distribution that is approximately normal. Using a 0.01 significance level, is there sufficient evidence to support the claim that the drug is effective in lowering systolic blood pressure?
Before
155
175
196
164
169
189
199
158
163
159
183
210
After
156
162
150
148
186
155
191
159
173
163
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! If one does a two sample t-test, the t-value is 1.75 with a p-value being 0.047 for a one way test (which is wanted here).
That is t df=20=(x1bar-x2bar)/sqrt{(s1^2/n1)+(s2^2/n2)}
A comment was made about paired sample data.
This study would be ideal for that, since each person would be his or her own control. Then the d, the difference would have its own mean, sd and fewer df.
The test might well be significant there BUT, there are 12 in sample 1 and 10 in sample 2. A paired t-test needs equal numbers in the two samples. If I removed 11 and 12 from sample 1, it is not significant, but there is no justification to do that other than mathematical.
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