Final answer:
The amount of variance in the outcome measures is inversely related to statistical power in a research study, as more variance makes it harder to detect a true effect.
Step-by-step explanation:
The factor from the provided options that is inversely related to statistical power in a research study is b. Amount of variance in the outcome measure(s). The statistical power of a study refers to the probability that the study will reject the null hypothesis when the alternative hypothesis is true. High power is desirable in statistical tests.
Options such as alpha level, magnitude of the effect size, and sample size are all directly related to power. Specifically, a lower alpha level increases the power, larger effect sizes increase power, and larger sample sizes also increase power. In contrast, more variance tends to decrease the power of a study because it makes it harder to detect a true effect. To counteract low power, statisticians might increase the sample size or take other measures to control variance.