Notes from Basic Statistical Practice 2: Sample Size
Power of a test
- Ability to find a difference in distribution when there really is a difference.
- Increase power of a test
o Increase size of alpha
§ If using 0.05, increase to say 0.01
§ Reduces risk of type 2 error, increases chance of type 1 error
- Reduce beta without increasing alpha
o Be more specific in prediction
o One tailed test more powerful than 2 tailed test
- Reduce overlap between 2 distributions
o Beta is reduced
o Difference between the means
o Size of std deviation.
- Look for strong, rather than subtle effects
- Improve sensitivity of the measure of dependent variable
- Planning sample sizes with power approaches – what sample size is required to achieve given power
- Different formula for factorial sample size
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