2: t-tests Flashcards
what does the levene’s test show?
checks whether several groups have the same variance in the population - We want a null hypothesis for levene’s
- If p ≤ .05 we reject null hypothesis (i.e. heterogeneity) - write this in write up
when do you used an paired t-test?
within participants/ repeated measures?
when do you use and independent t-test/
between participants/ independent groups
what contributes to variance between IV levels?
– Manipulation of IV (treatment effects)
– Individual differences
– Experimental error
* Random error
* Constant error
what contributes to variance within IV levels?
– Individual differences
– Experimental error
* Random error
how do you calculate the t-ratio?
variance between IV levels/ variance within IV levels
OR
mean difference/ estimated standard error (standard error difference on SPSS)
what are df for t-tests?
no. of samples-no. of parameters
within subjects = n-1
between subjects = (n-1)+(n-1) = n(total) - 2
what is cohen’s d?
The magnitude of difference
between two IV level means, expressed in
standard deviation units
how do you calculate cohen’s d?
difference between means/ average standard deviation
what are cohen’s d effect sizes?
small = 0.2
medium = 0.5
large = 0.8
what is the difference between cohen’s d & the t value?
cohen’s d ignores sample size & t quantifies the effect in the context of sample size
If you had a study with 1 IV, 2 levels and was a between participants deign, what statistical test would you use?
independent t-test
If you had a study with 1 IV, 2 levels and was a within participants deign, what statistical test would you use?
paired t-test
what is the non-parametric equivalent to the independent t-test?
mann-whitney u test
what is the non-parametric equivalent to the paired t-test?
wilcoxon t-test
