11. A researcher studies the effect of cognitive psychotherapy on positive self-

Question

11. A researcher studies the effect of cognitive psychotherapy on positive self-regard. The number of positive statements made about oneself is recorded for each participant during the first meeting. After eight weekly therapy sessions, the measures are repeated for each person. For the following data, determine whether there is a significant treatment effect, using a two-tailed test with = .05.

Participate Before Treatment After Treatment

A 7 10

B 6 13

C 9 12

D 5 8

H0: _____________ H1: _____________ df = _________ Critical region (tcrit): _____________ MD = ____________ s2 = _____________ SS = __________________ s(MD) = ________________ tobt = ________________ Decision (check one) ____ reject H0 ____ fail to reject H0 ____ Conclusion (check one) Cognitive psychotherapy did significantly affect positive self-regard ____ Cognitive psychotherapy did not significantly affect positive self-regard If appropriate, compute and evaluate Cohen’s d:

Explanation / Answer

H0: Congnitive psychotherapy did not significantly affect positive selef-regard

H1:Congnitive psychotherapy did significantly affect positive selef-regard

Degree of freedom df = n -1 = 4 - 1 = 3

Differences : -3 -7 -3 -3

Mean of Deffierences is -16/4 = -4

Sample Variance = { (-3-(-4)2 + (-7-(-4)2 + (-3-(-4)2 + (-3-(-4)2 }/3 = 4

SS = sqrt(sample variance) = sqrt(4) = 2

SE(MD)= s / sqrt(n) = 2/ 2 = 1

Test statistic tobs = MD/SE(MD) = -4

t critical value = -2.3534 at 5% los, 3df in left tail

Here tobs < tcrit and P value 0.0140 > alpah (0.05) we reject H0.

Thus Congnitive psychotherapy did significantly affect positive selef-regard

Cohen's D = |MD| / SD = 4 / 2 = 2

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