Your study
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Required sample
373
completed responses needed for your stated precision
Approaches to make
622
at your expected response rate — this is the number people forget
How to report it
What this assumes
Every sample size figure rests on assumptions, and an examiner may ask about them.
- p = .50. Maximum variability, the most conservative assumption. If you have a prior estimate of the proportion, the required sample falls.
- Simple random sampling. Cluster or stratified designs need a design effect adjustment, usually raising the figure.
- Finite population correction applied. This is why a population of 1,000 needs fewer responses than one of 100,000.
- Not for SEM. Structural equation modelling uses different rules — commonly 10 cases per estimated parameter, or a minimum in the 200 range.
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