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Chapter 70: Parametric Tests
Parametric tests provide inferences for making statements about the means of parent populations. A t-test is commonly used for this purpose. This test is based on the Student's t-statistic. The t-statistic assumes that the variable is normally distributed and the mean is known (or assumed to be known) and the population variance is estimated from the sample. Assume that the random variable X is normally distributed, with mean μ and unknown population variance σ2, which is estimated by the sample variance s2. Recall that the standard deviation of the sample mean, , is estimated as . Then is t distributed with n – 1 degrees for freedom.
The t-distribution is similar to the normal distribution in appearance. Both distributions are bell-shaped and symmetric. ...