Which combination would improve a study's power?

• A. Increase sample size and increase within-group variability
• B. Increase sample size and decrease within-group variability
• C. Decrease sample size and increase within-group variability
• D. Decrease sample size and decrease within-group variability

Answer: (B)

Power is the chance a study will detect a real effect when one exists. It climbs when you have more information and less noise. Increasing sample size provides more data points, which lowers the standard error and makes differences between groups easier to detect. Decreasing within-group variability tightens the clustering of data inside each group, so the true difference between groups stands out more against the random spread, boosting the test statistic and the probability of finding significance.

So combining a larger sample with tighter, less variable data within groups gives the strongest increase in power. The other scenarios either add noise relative to the sample size or reduce data, which dampens power even if variability is lower.