PSY340: Statistics for the Social Sciences

Part I:

1) In a planned study, here is a known population with a normal distribution, pop mean = 50, pop standard dev = 5. What is the predicted (standardized) effects size (d) if the researchers predict that those given an experimental treatment have a mean of
a) 50
b) 52
c) 54
d) 56
e) 47
For each part, also indicate whetehr the effect is approximately small, medium, or large.

2) For each of the following studies, make a chart of the four possible correct and incorrect decisions, and explian what each would mean.

a) A study of whether increasing hte amount of recess time improves school children's in-class behavior.
b) A study of whether color-blind individuals can distinguish gray shades better than the population at large.
c) A study comparing individuals who have ever been in psychotherapy to the general public to see if they are more tolerant of other people's upsets than is the general population.

3) Here is information about several possible versions of a planned experiment. Figure effect size and power for each; sketch the distributions involved, showing the area for alpha, beta and power (Assume all populations have a normal distribution).

	Population		Predicted Mean	N	alpha-level	1 or 2 tailed
	mean	std dev	(treatment)
(a)	90	4	91	100	0.05	1
(b)	90	4	92	100	0.05	1
(c)	90	2	91	100	0.05	1
(d)	90	4	91	16	0.05	1
(e)	90	4	91	100	0.01	1
(f)	90	4	91	100	0.05	2

4) On a particular memory task in which words are learned in a random order, it is known that people can recall a mean of 11 words with a standard deviation of 4, and the distribution follows a normal curve. A cognitive psychologist, to test a particular theory, modifies that task so that the words are presented in a way in which words that have a related meaning are presented together. The cognitive psychologist predicts that under these conditions, people will recall so many more words that there will be a large effect size. She plans to test this with a sample of 20 people, using the alpha level = 0.01 and a two tailed test.

a) What is the power of this study?
b) Sketch the distributions involved, showing the area for alpha, beta, and power.
c) Explain your answer to someone who understands hypothesis testing involving means of samples but has never learned about effect size or power.