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Z-testThe Z-test is a statistical test used in inference. The test requires the following to be known: Other conditions to be met include knowing that your sample mean from a simple random sample of the population. If the sample came from a different sampling method, a different formula must be used. It must also be known that the population varies normally (i.e., the sampling disribution of the probabilities of possible values fits a standard normal curve). If it is not known that the population varies normally, if suffices to have a sufficently large sample, generally agreed to be ≥ 30 or 40. In actuallity, knowing the true σ of a population is unrealistic, as it is impossible to measure every member of a population. It is more realistic to use a t-test, which uses the standard error obtained from the sample along with the t-distribution. The formula is as follows: -
External link Z test formula is actually as follows: z = (x - mu)/sigma
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