chap 11 Flashcards
What is a T-Test
A statistical “tool” used for looking at the difference in average scores of one or more variables between two groups that are mutually exclusive
What will a T-Test tell us
A) Is there a difference?
B) Is this difference Significant?
What are independent samples?
Groups that are completely separate
Groups are “independent” of one another.
Each participant is only tested once
ex: Males vs. Females
When to use the Independent Samples T-Test?
Each group is tested only once.
Only 2 Groups in Total
When interested in the difference between the group means
Assumptions of Independent T-Test
Observations are independent
Two populations must be “normal”
Two groups must have equal variance
-Homogeneity of Variance
Computing the T Test Statistic
Numerator is the Difference between the means.
Denominator is the amount of variance within and between groups.
How do I interpret computed T? p.353
Value from equation is the test statistic value (or obtained value).
with the t value, determine the critical value (the bar) for rejection of the null hypothesis
Degrees of Freedom?
Everything you need to know before you know the rest”
Or the no of entities in study that are “free to vary”
DF = N – 1 (for each group)
Two Tailed Test?
Two tailed tests-working off of a non-directional research hypothesis.
which “tail” to expect the difference in is unknown.
One tailed tests -working off of a directional research hypothesis.
Special Effects
Effect size is a measure of how different 2 groups are from one another
T-Test Tells us if they are significantly dif.
Effect Size gives us a better understanding as to HOW different – the magnitude
Computing the Effect Size
(Xbar1 – Xbar2) / St.Dev from either group How far are the means from one another Small = 0.0 - .20 Medium = .20 - .50 Large = .50 and above
