Lec 18 - Paired Samples T-Test

paired / dependent samples t-test

parametric test to determine differences between two sets of repeated measures data from one group of people - scores used might be from the same subject under different conditions

assumptions

1. the distribution of scores is normal or approximately normal

2. the dependent variable(s) are measured at interval or ratio levels

3. repeated measures data are collected from one group of subjects, resulting in paired scores

4. the differences between the paired scores are independent

one-sample crossover design

when one group of participants is exposed to one level of an intervention and then those scores are compared with the same participants’ responses to another level of the intervention resulting in paired scores

t calculation

-D = mean difference of the paired data

-S_D = standard error of the difference

standard error calculation

-S_D = standard deviation of the differences between the paired data

-n = number of subjects in the sample

paired t-test calculation steps (6)

1. calculate the difference scores

2. compute the mean

3. a) compute the standard deviation

   b) plug these numbers into the standard error formula

4. compute t value

5. compute degrees of freedom (n-1)

6. locate critical t and compare it to obtained t