Question

Dana uses the following parameters to determine that she needs a sample size of 140 participants for her study that will compare the means of two independent groups (t-test) using a one-tailed hypothesis:

Effect size (d) = .5

1. = .05
2. Power(1 - b) = .90

Using the above information, answer each of the following questions.

1. If Dana keeps alpha and sample size the same, but desires an effect size of .80, what will happen to power? Will it increase or decrease? Explain.
2. If Dana keeps the desired effect size and sample size the same, but reduces alpha to .025, what will happen to power? Will it increase or decrease? Explain.
3. If Dana keeps power and sample size the same, but increases the desired effect size to .8, what will happen to alpha? Will it increase or decrease? Explain.
4. Dana decides she wants to increase the desired effect size to 2.0 and increase the power to .99, but keeps alpha the same. She does so to increase the likelihood that an effect will be found, and to make sure her results demonstrate a large enough effect. Also, when she conducts her a priori power analysis to determine her sample size, she is excited to see that she needs far fewer participants in her sample with those parameters (target n = 18). What, if any, are the problems with Dana’s strategy?

Answer 1