# Answer to Question #814 in Statistics and Probability for Sara

Question #814

When we can use t-statistics instead of z-statistics?

Expert's answer

If & the population standard deviation is known, we use z-statistics, if it is unknown - t-statistics. When the size of the sample is large, the distribution of the data becomes closer to the Normal distribution and z-statistics can be used, in different sources N should be more than 30 or 50.

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