1. You are interested in determining whether an experimental birth control pull has the side effects of changing blood pressure. You randomly sample 10 women from the city in which you live. You give 5 of them a placebo for a month and then measure their diastolic blood pressure. Then you switch them to the birth control pill for a month and again measure their blood pressure. The other 5 women receive the same treatment except they are given the birth control pill first for a month, followed by the placebo for a month. The blood pressure readings are shown here. Note that to safeguard the women from unwanted pregnancy, another means of birth control that does not interact with the pill was used for the duration of the experiment.

Diastolic Blood Pressure

Subject No. Birth Control Pill Placebo

1 108 102

2 76 68

3 69 66

4 78 71

5 74 76

6 85 80

7 79 82

8 78 79

9 80 78

10 81 85

1. What is the alternative hypothesis? Assume a nondirectional hypothesis is appropriate.
2. What is the null hypothesis?
3. What is the value of t obtained.

d. What might we conclude using α = 0.05 _{2 tail} ?

e. What type error may have been made?

f. Calculate Cohen’s d.

2. Based on previous research and sound theoretical considerations, an experimental psychologist believes that memory for pictures is superior to memory for words. To test this hypothesis, the psychologist performs an experiment in which students from an introductory psychology class are used as subjects. Eight randomly selected students view 30 slides with nouns printed on them, and another group of eight randomly selected students views 30 slides with pictures of the same nouns. Each slide contains either one noun or one picture and is viewed for four seconds. After viewing the slides, subjects are given a recall test, and the number of correctly remembered items is measure. The data are shown here:

No. of pictures Recalled No. of nouns recalled

18 12

21 9

14 21

25 17

23 16

19 10

26 19

15 22

a. What is the alternative hypothesis?

b. What is the null hypothesis?

c. What is the value of t obtained.

d. What is the value of t-crit.

e. What might you conclude using α = 0.05 ₂ tail?

e. What type error might have been made?

f. Estimate the size of the real effect using omega squared and cohen’s d. Is the effect a large one?

1. A political candidate wishes to determine if endorsing increased social spending is likely to affect her standing in the polls. She has access to data on the popularity of several other candidates who have endorsed increased spending. The data was available both before and after the candidates announced their positions on the issue. The data are as follows:

Assuming no other factors were influencing the popularity ratings

a. State the nondirectional alternative hypothesis.

b. State the null hypothesis.

c. What is the value of t obtained.

d. What is the value of t critical.

d. What might the candidate conclude using α = 0.01 _{2 tail} ?

e. What type error might the candidate have made?

f. calculate cohen’s d

4. A nurse was hired by a governmental ecology agency to investigate the impact of a lead smelter on the level of lead in the blood of children living near the smelter. Ten children were chosen at random from those living near the smelter. A comparison group of seven children was randomly selected from those living in an area relatively free from possible lead pollution. Blood samples were taken from the children and lead levels determined. The following are the results (scores are in micrograms of lead per 100 milliliters of blood.

Lead Levels

Children living near smelter Children living in unpolluted area

18 9

16 13

21 8

14 15

17 17

19 12

22 11

24

15

18

a. What is the alternative hypothesis? Assume that a nondirectional hypothesis is warranted.

b. What is the null hypothesis?

c. What is the value of t obtained.

d. What is the value of t-critical.

d. What might the candidate conclude using α = 0.05 _{2 tail} ?

e. What type error might the candidate have made?

f. Estimate the size of the real effect using omega squared and cohen’s d. Is the effect a large one?

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