PSY 429 Experimental Psychology
Homework Exercise #1
Due: Thursday, September 28, 2000
PSY 429 Experimental Psychology
Homework Exercise #1
Due: Thursday, September 28, 2000
Directions: Please answer the following questions. Do your statistical work on a separate sheet of paper and write the answers on this sheet and staple your statistical work to this sheet. Please be neat and your writing legible.
1. How accurate are eyewitness reports of accidents? Behavioral scientists have studied this question in some detail. In one experiment, subjects viewed a film of an accident in which a car ran a stop sign and hit a parked car. The speed of the car was 30 miles per hour. After viewing the film, subjects were asked to estimate the speed of the car. Fifteen subjects gave the following estimates.
Subject Estimate in miles per hour
1. 16
2. 41
3. 32
4. 17
5. 36
6. 21
7. 39
8. 33
9. 29
10. 44
11. 18
12. 35
13. 25
14. 31
15. 25
a. Calculate the mean and the standard deviation for these data. How accurate were the estimates considering the mean score across all subjects? How does the standard deviation help to interpret the mean?
2. Suppose IQ scores in a population are approximately normally distributed with a mean of 110.00 and a standard deviation of 15.00. What proportion of individuals have IQ scores of
a. 110 or greater
b. 110 or less
c. between 95 and 120
d. 115 or less
e. 100 or greater
f. 100 or less
3. Lie detectors or polygraphs are used to help determine whether a person has knowledge of a crime. These devices are based on autonomic changes in the nervous system. The assumption is that lying will be reflected in physiological changes that are not under the voluntary control of the individual. Measurements of the individual's physiological response when asked certain questions can be used to make inferences about the verdicality or truth of his or her answers. Lie detection tests typically involve answering a series of neutral questions (for example, "What is your name?" or "Where do you work?") among which the critical questions are embedded. Consider the case where an individual has been asked a series of questions, including a critical item. Physiological measurements in the form of galvanic skin responses are taken for each question. The galvanic skin response scores approximate a normal distribution with a mean of 49.40 and a standard deviation of 3.00. For the critical question, the score was 57.50. Convert this into a standard score and draw a conclusion as to whether the subject was telling the truth or lying to the critical question.
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