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21.HE.B: Captopril is a drug designed to lower systolic blood pressure. When subjects were treated with this drug, their systolic blood pressure readings (in mm Hg) were measured before and after the...

21.HE.B: Captopril is a drug designed to lower systolic blood pressure. When subjects were treated with this drug, their systolic blood pressure readings (in mm Hg) were measured before and after the drug was taken. The results are in the accompanying table on the next page.

(a)      Go through “The Drill” for paired t-tests (Use a 0.05 α-level and the corresponding confidence interval.)

          The Drill:

  • Assumptions and Conditions
    • Paired Data Condition

The data must be paired. Only use pairing if there is a natural matching. The two-sample t-test and the paired t-test are not interchangeable.

Independence Assumption

For paired data, the groups are never independent. Need differences independent, not individuals Randomization ensures independence.

Normal Population Assumption

Need to assume the differences follow a Normal model.

  • One or two-sided?
  • α-level = 0.05
  • Statement of the Hypothesis
  • Distribution of the sample mean under Ho.
  • Make a picture
  • Mechanics – test statistic
  • p-value
  • Interpretation in context
  • Conclusion
  • Type I and Type II error

(b)      What p-value do we get if we choose the (incorrect) two-sample test of Chapter 20 instead of the (correct) paired t-test? Will it affect the conclusion?

A

B

C

D

E

F

G

H

I

J

K

L

Before

200

174

198

170

179

182

193

209

185

155

169

210

After

191

170

177

167

159

151

176

183

159

145

146

177

0 0
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Answer #1

Paired Data Condition

The data must be paired. Only use pairing if there is a natural matching.

For paired data, the groups are never independent.

Normal Population Assumption

Following table shows the calculations:

Before After d=before-after (d-mean)^2
200 191 9 44.89
174 170 4 2.89
198 177 21 349.69
170 167 3 0.49
179 159 20 313.29
182 151 31 823.69
193 176 17 216.09
209 183 26 561.69
185 159 26 561.69
155 145 10 59.29
169 146 23 428.49
210 177 33 942.49
Total 223 4304.68

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media%2Fbc6%2Fbc605ce8-8e3f-4320-864f-f2

Conclusion We cannot conclude that Captopril drug lowers systolic blood pressure..

Since we fail to reject the null hypothesis so type II error is possible.

(B)

Following is the output of independent sample t test:

Hypothesis Test: Independent Groups (t-test, pooled variance)
Before After
185.33 166.75 mean
17.07 14.86 std. dev.
12 12 n
22 df
18.583 difference (Before - After)
256.133 pooled variance
16.004 pooled std. dev.
6.534 standard error of difference
0 hypothesized difference
2.84 t
.0047 p-value (one-tailed, upper)
F-test for equality of variance
291.33 variance: Before
220.93 variance: After
1.32 F
.6544 p-value

So the p-value is: 0.0047

In this we reject the null hypothesis and conclude that Captopril drug lowers systolic blood pressure..

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