Consider the following study that is being planned:

·      μ = 95, σ = 4, predicted mean = 98, N = 30, α = .01, two-tailed test

a. Compute the effect size

b. Compute the power

c. If you wanted to plan a study with the conventional minimum power, what is the best variable to change in order to increase power?

For a given study, how do each of the following variables affect power?

a. Changing α from .05 to .01

INCREASE / DECREASE / NO CHANGE

b. Increasing the sample size

INCREASE / DECREASE / NO CHANGE

c. Increasing the effect size

INCREASE / DECREASE / NO CHANGE

d. Choosing a research hypothesis with a value closer to the null hypothesis

INCREASE / DECREASE / NO CHANGE

e. Changing from a one-tailed test to a two-tailed test

INCREASE / DECREASE / NO CHANGE

A researcher is evaluating the influence of a treatment using a sample selected from a normally distributed population with a mean of u = 80 and a standard deviation of o = 20. The researcher expects a 12-point treatment effect and plans to use a two-tailed hypothesis test with a .05.

a. Compute the power of the test if the researcher uses a sample of n = 16 individuals. (See Example 8.6.)

b. Compute the power of the test if the researcher uses a sample of n = 25 individuals

 Consider the following data and corresponding weights.

a.Compute the weighted mean.

b. Compute the sample mean of the four data values without weighting. Note the difference in the results provided by the two computations.