PSYC 331 Lecture 18 -- Related t-test

# PSYC 331 Lecture 18 -- Related t-test - PSYC 331 Lecture 18...

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1 PSYC 331 Lecture 18 The t-statistic for Two Related Samples

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2 Overview In this lecture, we will… Learn about the t -test for Related Samples in terms of: Similarities to the single sample t-test Differences and similarities between repeated measures and matched subjects design Hypothesis tests Effect size Benefits and problems Assumptions
3 What is a dependent measures study? Repeated measures design Single sample Each individual is measured more than once on the same DV Same subjects are used in all treatment conditions Matched-subjects design More than one sample Each subject is matched to another subject in a different group (equivalent with respect to a control variable).

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4 t statistic for related samples Uses difference scores difference score = D = X 2 – X 1 How would you find a Mean Difference? Let’s try using the following scores: Person Before Treatment After Treatment Difference A 20 40 ? B 15 35 ? C 18 26 ? D 40 42 ?
5 Mean Difference The sum of the differences divided by the number of scores M D = ∑D n

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6 Comparison of related samples t to single sample t Formula is similar to the single sample t: Remember: Where s M is calculated exactly as s M was except that here you use the difference score… sample statistic – population parameter estimated standard error = M - μ s M = Single sample t Related sample t = sample statistic – population parameter estimated standard error = M D - μ D s M D D
Calculation of s M Remember for a single-sample t, the estimated standard error is: For repeated measures (and matched subjects) we use the same formula Just that this s 2 is calculated using the difference scores. D

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## This note was uploaded on 01/15/2010 for the course PSYC 331 taught by Professor Dianealonso during the Fall '09 term at UMBC.

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PSYC 331 Lecture 18 -- Related t-test - PSYC 331 Lecture 18...

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