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Why is it not necessary to have/use a standard deviation when performing a t-test but you need one with a z-test?

If you were to add one step to better understand the five-step process, what would that be? How would it make the calculations, or process, easier?

https://brainmass.com/statistics/quantative-analysis-of-data/standard-deviation-performing-test-210371

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The response address the queries posted in 443 words with references.
//The given discussion paper is based on the two 'Parametric Tests', which are the't-test' and 'z-test'. In this series, in the first section of the discussion paper, the use of these two tests, in order to have the standard deviation, is explained in detail.//

Parametric test: t-test and z-test

It is not necessary to have a standard deviation while performing a t-test because the null hypothesis does not depict the true value of the standard deviation. Another crucial reason is that the population variance is not known and the sample size of the population is too small I.e. N<30it means that inferences are not normally distributed. The key reason is that the estimate ...

#### Solution Summary

The expert examines standard deviation when performing a t-test. The response address the queries posted in 443 words with references.

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