Power: The probability of correctly identifying a difference between the two groups in the study sample when one genuinely exists.
Lowest acceptable is usually 80% (meaning 8/10 chance of detecting the difference you are trying to detect, and 2/10 chance of missing a true difference.)
In general, power is increased by having larger sample size. To calculate sample size required for your study, you need:
- an estimate of what entails a true difference between your groups (from prior studies)
- standard deviation of outcomes (from prior studies)
- power level you want
- p-value you want