Read Chapter 9

Do pages 295-6 # 1,2,3,5,6,10, 13SHOW ALL WORK

1. Under what circumstances is a t-statistic used instead of a z-score for a hypothesis test?

1. A sample of n = 16 scores has a mean of M = 56 and a standard deviation of s = 12.

a) Explain what is measured by the sample standard deviation.

b) Compute the estimated standard error for the sample mean and explain what is measured by the standard error.

1. Find the estimated standard error for the sample mean for each of the following samples.
2. N=9 with SS=1152
3. N=16 with SS=540
4. N=25 with SS=600

1. Find the t values that form the boundaries of the critical region for a two-tailed test with a = .05 for each of the following sample sizes:

a. n=4

b. n=15

c. n=24

1. Find the t value that forms the boundary of the critical region in the right-hand tail for a one-tailed test with

a = .01 for each of the following sample sizes.

a. n=10

b. n=20

c. n=30

10. A random sample of n = 25 individuals is selected from a population with = 20, and a treatment is administered to each individual in the sample. After treatment, the sample mean is found to be M = 22.2 with SS = 384.

1. How much difference is there between the mean for the treated sample and the mean for the original population? (Note: In a hypothesis test, this value forms the numerator of the t statistic.)

1. If there is no treatment effect, how much difference is expected between the sample mean and its population mean? That is, find the standard error for M. (Note: In a hypothesis test, this value is the denominator of the t statistic.)

1. Based on the sample data, does the treatment have a significant effect? Use a two-tailed test with

a = .05.

13.The spotlight effect refers to overestimating the extent to which others notice your appearance or behavior, especially when you commit a social faux pas. Effectively, you feel as if you are suddenly standing in a spotlight with everyone looking. In one demonstration of this phenomenon, Gilovich, Medvec, and Savitsky (2000) asked college students to put on a Barry Manilow T-shirt that fellow students had previously judged to be embarrassing. The participants were then led into a room in which other students were already participating in an experiment. After a few minutes, the participant was led back out of the room and was allowed to remove the shirt. Later, each participant was asked to estimate how many people in the room had noticed the shirt. The individuals who were in the room were also asked whether they noticed the shirt. In the study, the participants significantly overestimated the actual number of people who had noticed.

a. In a similar study using a sample of n = 9 participants, the individuals who wore the shirt produced an average estimate of = 6.4 with SS = 162 . The average number who said they noticed was 3.1. Is the estimate from the participants significantly different from the actual number? Test the null hypothesis that the true mean is = 3.1 using a two-tailed test with a=.05

b.Is the estimate from the participants significantly higher than the actual number ( = 3.1 )? Use a one-tailed test with a = .05 .