What is the commonly accepted threshold for power in a study?

What is the commonly accepted threshold for power in a study?

• A. 0.50
• B. 0.80
• C. 0.95
• D. 0.99

Answer: (B)

Power is the probability that a study will detect an effect if there truly is one. It’s 1 minus the probability of a type II error (failing to reject the null when the alternative is true). The commonly accepted target for power is 0.80, meaning an 80% chance of detecting the effect when it exists. This level offers a practical balance: it keeps the risk of missing real effects reasonably low while avoiding the need for prohibitively large sample sizes. Higher power, like 0.95 or 0.99, would require much larger samples or larger effects and is often impractical. Lower power, such as 0.50, gives a coin-flip chance of missing real effects. In practice, researchers plan designs to reach around 0.80 power by choosing appropriate sample size, anticipated effect size, and significance level.

Power is the probability that a study will detect an effect if there truly is one. It’s 1 minus the probability of a type II error (failing to reject the null when the alternative is true). The commonly accepted target for power is 0.80, meaning an 80% chance of detecting the effect when it exists. This level offers a practical balance: it keeps the risk of missing real effects reasonably low while avoiding the need for prohibitively large sample sizes. Higher power, like 0.95 or 0.99, would require much larger samples or larger effects and is often impractical. Lower power, such as 0.50, gives a coin-flip chance of missing real effects. In practice, researchers plan designs to reach around 0.80 power by choosing appropriate sample size, anticipated effect size, and significance level.