Paired samples t-tests Flashcards
What does a t-test tell us?
The t test tells us how likely it is that we will observe a difference - is this by chance?
why would we use a t test?
when one of our variables has more than one condition.
what kind of data design must we have to do a t-test?
repeated design
how many conditions must our IV have to do a t test?
2
How many participants do you need to do a t-test?
10
What scale should our data be on to use a t-test?
interval/ratio
The difference scores (change scores) for t tests must be…
Normally distributed :)
T tests are interested in the __________ between participant’s T1 and their T2 scores.
differences
When will the t value get bigger?
- when the difference scores are larger, assuming they are also consistently in the same direction.
- when there is less variation in difference scores.
___ variation is more likely to be significant as there is a much smaller distribution, this score is an extreme.
less
t (951) = -12.39, p< .001 (two tailed)
Anything missing?
Yes effect size!
If you use a 1 tailed hypothesis what do you have to do to the p value?
We have to half it!
what is a small effect size?
0.1
What is a medium effect size?
0.3
What is a large effect size?
> 0.5
What is the formula for r (effect size)?
√ t2/ (t2 + df)
t = -12.39 df= 951
Calculate the effect size.
√ t2/ (t2 + df)
√-12.39 squared/ (-12.39 squared + 951)
r = 0.37
Larger T value =…
larger difference and smaller variation
What do t-tests evaluate?
The difference in participants’ scores from one condition to the other.
What 2 non-parametric tests would you use?
2 conditions: Wilcoxon Signed ranks
3 or more conditions: Friedman Test
if you have 2 conditions what non-parametric test do you use?
Wilcoxon Signed Ranks
If you have 3 conditions or more, what non-parametric test do you use?
Friedman Test
What is the non-parametric equivalent to the t-test?
Wilcoxon signed Ranks
what conditions does non-parametric data reflect?
Less than 10 participants
Ordinal data
Data skewed
