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t-tests6slidesperpage.pdf

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KPED 4320

 Independent variable  Catagorical (nominal or ordinal)  Numerical (interval or ratio)

 Dependent variable  Catagorical (nominal or ordinal)  Numerical (interval or ratio)

 One group (one sample) t-test: Compares sample mean to a hypothesized population mean

 Dependent (paired samples) t-test: Compares two sample means from the same group of subjects  e.g., test & retest or before and after

 Independent (Unpaired) samples t-test: Compares sample means of the same variable from different groups  e.g., experimental vs. control or group 1 vs. 2

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Examples:  Independent t-test  Flexibility differences between girls and

boys

 Dependent t-test  Pre and Post strength measurements after

6 weeks of training on the Total Gym

A t-test is performed to compare the actual difference between the means of two samples with the difference expected if only chance were operating.

 Test performed on 2 independent samples  experimental group  treatment group

 If the t-ratio exceeds the critical ratio, the null hypothesis is rejected.  Chance is rejected and probable cause is assumed.

 If the t-ratio does not exceed the critical ratio, the null hypotheses is accepted.  The mean difference is insignificant.

t value = Difference between group means

Variability of groups

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 DV: Interval or ratio

 DV: Normal distribution

 IV: Nominal (can only compare two means)

 Mutually exclusive groups

 Random selection or assignment