Psych Test 3 Flashcards
What is the assumption of homogeneity of variance?
An assumption in which the population variances of two or more samples are equal
How many degrees of freedom are appropriate for each of the tests we’ve discussed?
- Independent Sample T Test= n1-n2-2
- Paired T Test= # of different scores -1
- ANOVA: dfbetween & df within
What is the difference between a between-subjects design and a within-subjects design?
Between-subjects study design: different people test each condition, so that each person is only exposed to a single user interface.
Within-subjects study design: the same person tests all the conditions
Why is it preferable to use an ANOVA rather than multiple t-tests to make comparisons among multiple levels of an independent variable?
Each time you run a t-test, you’ll inherit a Type-I error.
Your overall error rate is proportional to the number of individual t-test that you run. The more you do, the more likely you will get a false positive.
What are the null and alternative hypotheses for the ANOVA?
Null Hypothesis: H0: there is no difference in means
Alternative Hypothesis: HA: at least one of the population means is different than the others
What does it mean to partition the variance in ANOVA? How is the variance partitioned in the one-way ANOVA?
we could divide the total variance in our data into the various sources of that variation.
in 4 ways
What are MSbetween and MSwithin?
MSbetween: consists of the population variance plus a variance produced from the differences. between the samples. MSwithin: is an estimate of the population variance.
Since variances are always positive, if the null hypothesis is false, MSbetween will be larger than MSwithin.
Why does the F ratio reveal whether or not there is an effect of the independent variable?
The f ratio reveals that there is more variability between the groups (caused by the independent variable)
If there is no effect of the independent variable, what F value would you expect? Why?
If there is no effect (the null is true), the f ration should be one or close to one
What are the properties of the F distribution?
The F distribution is either zero or positive, so there are no negative values for F
Why is it necessary to run multiple comparisons following the ANOVA?
Multiple comparison conduct an analysis of all possible pairwise means
What is the difference between planned and post-hoc comparisons? When should each be used?
Planned Comparisons should be used when the comparisons are planned prior to running the experiment AND there are relatively few comparisons.
Post-hoc comparisons should be used when: the comparisons are not planned prior to running the experiment OR there are many comparisons
Why are post-hoc comparison methods preferred when making many comparisons?
To control the experiment wise error rate by reducing there statistical power of the comparisons and to identify exactly which groups differ from each other
How are the ANOVA and t-test related?
Both the t-test and the ANOVA have the same assumptions: normality and homogeneity of variance. They both should give the same answers.
ANOVA is just a generalization of t-test.
