Related T-tests Flashcards
What is a related t-test?
This is used for data retrieved from repeated measures/within-participants design.
Also known as correlated/paired t-test
What are the two different research designs that a paired t-test is used for?
Repeated design: one sample, tested at two different times.
Matched design: two samples matched on relevant variables.
What is a t-test?
It compares the mean of two different sets of scores.
It is used to see whether the average of one group is significantly different from another group.
What are the two possible sources of variance?
The IV - difference between the two means
Error variance - uncontrolled factors
Why is error variance reduced in a related t-test?
Because we are using related design data which has been collected from either the same participants or participants who have been carefully matched.
Does related scores give us more control over the variance?
Yes
What is Counterbalancing?
This is used, whenever possible, in repeated design. It is used because there is a risk when testing the same group that their performance may improve due to familiarity or learning.
What we do is counterbalance the conditions
E.g. Make half the participants be the control and the other half be the experimental the first time then switch for the second time.
What is the data requirements for the related t-test?
Two sets of data from continuous variables.
From repeated/matched design
Data should be correlated
Data should form a normal distribution.
What variables are needed for the related t-test?
1 categorical IV and 1 continuous DV
How is the t-score in a related t-test calculated?
Particular sample mean - average of sample means
divided by the standard error of sample means.
How do we do a related t-test with two samples?
Process is identical but we need to convert the means from our two groups into a single value. To do this we simply subtract the second test from the first to get the D score. Then we work out the standard error for D.
To get the t score we divide the mean of D by the standard error or D.
How to do a related t-test in SPSS?
Analyze -> compare means -> paired samples t-test
Then place two variables in the paired variables box in the same row.
