Gastric freezing was once a recommended treatment for ulcers in the upper intest
ID: 3232356 • Letter: G
Question
Gastric freezing was once a recommended treatment for ulcers in the upper intestine. Use of gastric freezing stopped after experiments showed it had no effect. One randomized comparative experiment found that 23 of the 77 gastric-freezing patients improved, while 25 of the 73 patients in the placebo group improved. We can test the hypothesis of "no difference" between the two groups in two ways: using the Two Sample Z Test for a difference in proportions or using the Chi-Square Test of independence. (a) Present the data in a 2 times 2 table. We will start by using the Two Sample Z Test for a difference in proportions. (b) State the hypotheses (use a two-sided alternative): H_0: P_1 H_a: p_1 (c) The test statistic is z =. (Use 2 decimal places) (d) The p-value is. (Use 4 decimal places) Now we will use the Chi-Square Test of Independence to test the hypothesis from (b). (e) The test statistic chi^2 =. (Use 4 decimal places) (f) The p-value is. (Use 4 decimal places) Note that the chi_2 test statistic is the square of the z test statistic, and the p-values are almost identical (they are slightly off due to roundoff error from using the Z table). (g) What do you conclude about the effectiveness of gastric freezing as a treatment for ulcers? (Use alpha = 0.05.) Gastric freezing is an effective method. Gastric freezing is not an effective method.Explanation / Answer
a)
Improved
Did not improve
Total
proportion
Gastric-freezing
23
54
77
0.298701299
Placebo
25
48
73
0.342465753
b)
H0:p1=p2
H1:p1#p2
c)
ZSTAT=(p1-p2)-(1 – 2)/p(1-p)(1/n1+1/n2)
=(0.2987-0.3425)-0/0.32(0.68)(1/77+1/73)
=(-0.0437645)/0.07620234
=-0.57
d)
The P-Value is 0.568678.
The result is not significant at p < 0.05.
Improved
Did not improve
Total
proportion
Gastric-freezing
23
54
77
0.298701299
Placebo
25
48
73
0.342465753
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