When σ is unknown, one should use an estimate that is considered to be at least as large as the true σ. This will provide a conservative sample size to be on the safe side.

Question

Quizplus · Accepted Answer

Using an estimate of σ that is at least as large as the true σ ensures that the calculated sample size is sufficiently large to achieve the desired power for a statistical test, thus providing a conservative approach to sample size determination.

When σ Is Unknown, One Should Use an Estimate That