Week_7_2_group_t_test

# Week_7_2_group_t_test - SAN JOS STATE UNIVERSITY College of...

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SAN JOSÉ STATE UNIVERSITY College of Social Work S. W. 242 Spring 2008 Edward Cohen Week 7: March 7, 2008 Chi-Square Lab Comparing means of two groups: t -tests (+ some introductory material on Confidence Intervals) On a Snapple bottle top: “Americans on average eat 18 acres of pizza every day.” What is the average they might be talking about? What kind of an American eats 18 acres of pizza every day? Concepts you should know: Z scores Confidence interval of the mean Standard error of the mean Critical values Type I and Type II errors Assumptions for using t -test Equality of variances Independent group t -test Dependent group t -test Degrees of freedom (and the t -test) Confidence interval of the difference between means I. Z Scores and Confidence Intervals A. Z score — a transformation of the raw score (interval/ratio level variable) that tells how many standard deviations the score lies from the mean 1. Formula: (raw score – mean) divided by the sample standard deviation 2. In a large number of randomly selected samples, 2.5% of their means would fall within two standard deviations above population the mean (z score = +

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Week_7_2_group_t_test - SAN JOS STATE UNIVERSITY College of...

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