But because the hypothesized difference between the populations is 0, the order of the samples in this computation is arbitrary- could just as well have been the female sample mean and the male sample mean, in which case z would be 2.37 instead of –2.37. The computed z‐value is negative because the (larger) mean for females was subtracted from the (smaller) mean for males. What is the likelihood that the population means of concentrations of the element are the same for men and women? Random samples of 75 male and 50 female donors yield concentration means of 28 and 33 ppm, respectively. The amount of a certain trace element in blood is known to vary with a standard deviation of 14.1 ppm (parts per million) for male blood donors and 9.5 ppm for female donors. Where and are the means of the two samples, Δ is the hypothesized difference between the population means (0 if testing for equal means), σ 1 and σ 2 are the standard deviations of the two populations, and n 1and n 2are the sizes of the two samples. Online Quizzes for CliffsNotes Statistics QuickReview, 2nd Edition.Quiz: Test for Comparing Two Proportions.Quiz: Test for a Single Population Proportion.Test for a Single Population Proportion.Quiz: Two-Sample t-test for Comparing Two Means.Two Sample t test for Comparing Two Means.Quiz: Two-Sample z-test for Comparing Two Means.Quiz: Introduction to Univariate Inferential Tests.Two-Sample z-test for Comparing Two Means.Quiz: Point Estimates and Confidence Intervals.Point Estimates and Confidence Intervals.Quiz: Normal Approximation to the Binomial.Quiz: Populations, Samples, Parameters, and Statistics.Populations, Samples, Parameters, and Statistics.Quiz: Introduction to Numerical Measures.
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