T-Test and non parametric
14 important questions on T-Test and non parametric
What do you use a dependent t-test for? What is h0?
H0= no effect or differences between groups or conditions
How do you interpret the t value?
Compare obtained t-value against max t value we would expect to occur if there was no effect in the population, in at distribution with the same dof
if p<0,05 reject h0
Why is effect size important?
Measures of effect size:
Cohen's d
Pearsons r
Odds ratio
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How do you interpret pearsons r?
r= 0,3 Medium effect (9% variance explained)
r= 0,5 large effect (25% variance explained)
How do you report t-test in methods section?
The test
95% CI
Pearson's R
What are assumptions of the independent t-test?
Data measured at least at interval level
The variance of the dependent variable is equal in the populations being investigated (homogeneity of variance)
Scores are independent (from different people)
What does non-parametric mean? How does it work?
Works by ranking the data,
Lowest score gets a 1, next highest a 2 and so on. Analysis then happens on the rank instead of data
What is a non-parametric equivalent of the independent t-test?
Mann-whitney test
What do you report in non-parametric tests instead of the mean and sd?
Dependent paired t-test
Same subjects measured twice or matched paired design
Use difference scores in your analysis
NHST=null hypothesis significance testing, null Hp=difference equals to 0
if t value is high --> your model is most likely better than the noise -->significant difference(p<.05), null Hp rejected
if low t value--> your model as good as the noise --> no much difference between the differences, accepted null hp
Independent t test equation (equal sample size)
Before running ANOVA what are the assumptions for parametric test to be checked?
Interval data
Normality
Homogeneity of variance
Post hoc procedure for ANOVA
It allows pairwise comparison between group differences/means
Doing several t-test with control of family wise error
Recommended Tukey, not Bonferroni
What if Levene's test is significant in ANOVA?
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