# lab3 - Dependent Samples t-test The two samples you are...

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1 Dependent Samples t -test • The two samples you are comparing have some relationship to each other. – Pre- and post-treatment measures – Matched pairs • Why use this design instead of independent samples? – Efficiency of subjects – Decrease variability in sample • Implies a smaller standard error and therefore, a larger t – Study change over time Y X Y X Y X s σ ρσ + = 2 2 How to test? • First, you should recognize that the unit of observation is the pair of results. – Each individual subject’s (or matched pair’s) observations must be kept together. • Because the unit of observation is the pair of results, you can do a one-sample t -test on difference scores. – For an independent samples -test, we were examining the difference in means . – Here, we are examining the mean difference . 0 : 0 = Y X H µ 0 : 0 = D H Example • Does meditation influence stress? • Measure heart rate as an indicator of stress before and after meditation 70 75 5 73 81 4 71 80 3 71 78 2 71 70 1 X 2 X 1 Subject After Before Example, con’t

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## This note was uploaded on 07/17/2008 for the course PHYS 321 taught by Professor Zandt during the Spring '05 term at Ohio State.

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lab3 - Dependent Samples t-test The two samples you are...

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