Lecture 14_dependent samples t-test

Lecture 14_dependent samples t-test - 10/20/2010 Dependent...

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10/20/2010 1 Dependent Samples t-test 1 Review • We have now gone over several different statistics that test mean differences… – The one-sample z-test compared a sample mean to a known population μ and σ – The one-sample t-test compared a sample mean to a known population mean and an unknown standard deviation 2 Review • These tests follow the same basic logic… you want to test whether a mean significantly differs from another mean 3 X M X s μ M t X M X σ μ M z
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10/20/2010 2 Overview • The dependent t-test tests for differences in two means measured from the same sample • Used with repeated measures designs where subjects are measured on more than 1 occasion: prior to treatment (pre-test) and subsequent to treatment (post-test) • Means compared in the test are correlated because they come from the same person Overview • No information about the population is required for the dependent t-test • Test whether the treatment had an effect by comparing a subject’s pretest mean to their posttest mean and looking at the difference of the means – Each subject acts as their own control (there are not separate treatment and control groups) 5 Example Research Questions • Do students do better on computer- administered or paper and pencil tests? – Same students take both tests • Does return speed in pro tennis players differ between dominant and non- dominant arms? – Examine same group of pro-tennis players • Are there differences in reading and math scores for children in a school district? – Same children take both tests
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10/20/2010 3 Research Scenario • The Kaplan test preparation company wants to demonstrate that their study course will significantly increase scores on the Law School Admissions Test (LSAT). To test this hypothesis, a sample of 30 individuals are administered an LSAT pre- test upon enrolling in the course. The participants subsequently complete the Kaplan course, and are administered the LSAT a second time. Research Question • If we were conducting this study, we could write the research questions as: • “Are there differences in the mean LSAT scores prior to and following enrollment in a Kaplan study course?” • The research hypothesis is that LSAT scores will increase following participation in the Kaplan course Difference Scores • The focus of the dependent t-test is on
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Lecture 14_dependent samples t-test - 10/20/2010 Dependent...

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