Which of the following can increase power?

Which of the following can increase power?
a. Increasing standard deviation
b. Decreasing standard deviation
c. Increasing both means but keeping the difference between the means constant
d. Increasing both means but making the difference between the means smaller


b. Decreasing standard deviation

1. Power increases if the standard deviation is smaller.
2. If the difference between the means is bigger, the power is bigger.
3. Sample size increase also increases power