A psychologist wants to test whether or not gratitude would significantly increa

Question

A psychologist wants to test whether or not gratitude would significantly increase helping behaviors. Students in the control group are asked to write a neutral essay about what they had for breakfast today. Students in the experimental group write a gratitude-inducing essay about their past experience of being helped by someone. After participants finish writing an essay and respond to a questionnaire, the researcher tells them that she needs help folding and inserting a bunch of letters into envelopes and would highly appreciate if the participant can help. The researcher records the number of completed envelopes as the indicators of helping behaviors. The data are presented below.Control (write neutral essay): 15, 22, 20Experimental group (write gratitude essay): 39, 49, 50What is the value and size of this effect?

-5.4; small

Explanation / Answer

Solution:

SD (pooled) = (SD1^2 + SD^2)/2

SD (pooled) = (3.60555 + 6.08276)/2

SD (pooled) = 4.844

Cohen's d effect = (M1 - M2)/SD (pooled)

Cohen's d effect = (19 - 46)/4.844 = -5.4

It is a large effect size.

Control Experiment 15 39 22 49 20 50 Mean 19 46 Standard deviation 3.605551 6.08276253

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