Definition of z–test
: any of several statistical tests that use a random variable having a z distribution to test hypotheses about the mean of a population based on a single sample or about the difference between the means of two populations based on a sample from each when the standard deviations of the populations are known or to test hypotheses about the proportion of successes in a single sample or the difference between the proportion of successes in two samples when the standard deviations are estimated from the sample data
First Known Use of z–test
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