If the sample size be less than 30 with known sigma, which test will be more appropriate, Z or t?

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Raid Amin

If sigma is known, then use a z test, but when is sigma really known for sure?

Muayyad Ahmad

you can use G. power to calculate sample size in ttest. depend on the effect size, if the result less than what you have, then the risk of type II error is present. thus, you may go to nonparametric test.

If n