Module 18: The T-Test for Independent Groups

Question 1

Conceptual formula t-test

Answer 1

t = (sample difference - expected difference (H0)) / standard error of the difference

Question 2

Independent-groups t-test

Answer 2

is a parametric statistical test that compares the performance of two different samples of participants. It indicates whether the two samples perform so similarly that we conclude that they are likely from the same population or whether they perform so differently that we conclude that they represent two different populations.

Question 3

Standard error of the difference

Answer 3

The standard deviation of the sampling distribution of differences between the means of independent samples in a two-sample experiment.

Question 4

Degrees of freedom

Answer 4

the number of scores in a sample that are free to vary, that for an independent-groups t test is N – 2. Example: N is for participants, so with 20 participants, the df is 20-2=18. So, 18 degrees of freedom

Question 5

Effect size

Answer 5

the proportion of variance in the dependent variable that is accounted for by the manipulation of the independent variable. Effect size indicates how big a role the conditions of the independent variable play in determining scores on the dependent variable.

E.g. Cohen’s d

Question 6

Cohen’s d

Answer 6

Cohen’s d is an inferential statistic for measuring effect size.
• Small at least 0.20
• Medium at least 0.50
• Large at least 0.80