T-Tests, ANOVAS, ANCOVAS

Question 1

T-Tests are:

Answer 1

1. Test whether the regression coefficient (b), is significantly different from zero
2. Provides some idea of how well a predictor predicts the outcome variable
3. Can be used to see whether a predictor variable makes a statistically significant contribution to the regression model

Question 2

Independent T-Test

Answer 2

Tests for differences between means of groups containing different participants when the sampling distribution is normal, the groups have equal variances and data are at least interval

Question 3

Paired Samples T-Test

Answer 3

1. Same participants take part in both experimental conditions
2. Ought to be less unsystematic variance compared to the independent t-test
3. Other things being equal, you do not need as many participants as you would for an independent samples design

Question 4

T Distribution becomes closer to normal when…

Answer 4

Degrees of freedom increase

Question 5

One-Sample T Test Assumptions

Answer 5

IV is continuous, independent scores, normal distribution, homogeneity of variances

Question 6

One- Sample T Test

Answer 6

Compares the mean of the sample data to a known value (IQ of class compared to IQ of society)

Question 7

Independent Sample T-Test Assumptions

Answer 7

Independence of groups, normal distribution, equal variances, homogeneity of variances, DV is interval or continuous, IV is categorical

Question 8

Independent Samples T-Test

Answer 8

Most common form of T Test
Compares the differences between the means of groups containing different participants when the sampling distributions is normal, the groups have equal variances, and data are at least interval

Question 9

Paired T Test Assumptions

Answer 9

DV is continuous, related samples, normal distribution

Question 10

Paired T Test

Answer 10

Compares the means between two related groups on the same continuous, dependent variable (same group will be used in both trials)

Question 11

ANOVA stands for…

Answer 11

Analysis of variance

Question 12

When should ANOVA be used?

Answer 12

if you are comparing more than 2 groups

Question 13

Family Wise Error

Answer 13

alpha level is our probability of rejecting the null hypothesis when the null hypothesis is true

Question 14

How can you avoid/minimise family wise error?

Answer 14

adjusting the alpha level by (finish on slide)

Question 15

Bonferroni test, tests what?

Answer 15

Guarantees control over type 1error, test to investigate which groups differ in a 1-way ind ANOVA

Question 16

When the between-groups variance is a lot larger than the within-groups variance, the F-value is ____ and the likelihood of such a result occurring because of sampling error is _____

Answer 16

large; low

Question 17

Imagine you compare the effectiveness of four different types of stimulant to keep you awake while revising statistics using a one-way ANOVA. The null hypothesis would be that all four treatments have the same effect on the mean time kept awake. How would you interpret the alternative hypothesis?

Answer 17

At least two of the stimulants will have different effects on the mean time spent awake

Question 18

An experiment was done to look at whether different relaxation techniques could predict sleep quality better than nothing. A sample of 400 participants were randomly allocated to one of four groups: massage, hot bath, reading or nothing. For one month each participant received one of these relaxation techniques for 30 minutes before going to bed each night. A special device was attached to the participant’s wrist that recorded their quality of sleep, providing them with a score out of 100. The outcome was the average quality of sleep score over the course of the month.

Which test could we use to analyse these data?

Answer 18

Regression or ANOVA

Question 19

Differences between group means can be characterized as a regression (linear) model if:

Answer 19

The experimental groups are represented by a binary variable (i.e. code 1 and 0).

Question 20

Other things being equal, compared to the paired-samples (or dependent)t-test, the independent-test:

Answer 20

Has less power to find an effect.

Question 21

Standard error…

Answer 21

It is the standard deviation of the sampling distribution of a statistic

Question 22

In t-distribution, as the df increase the distribution becomes closer or further away from normal

Answer 22

closer

Question 23

Partial eta squared is reported for…

Answer 23

ANOVA and ANCOVA

Question 24

Assumptions of ANOVA

Answer 24

1. Independence of data
2. DV is continuous, IV is categorical
3. No significant outliers
4. DV is approximately normally distributed for each category of the IV

Question 25

ANCOVA is an extension of…

Answer 25

Multiple Regression

Question 26

ANCOVA allows you to test…

Answer 26

All the regression lines to see which have different intercepts as long as all your slopes are equal

Question 27

Unlike an ANOVA and ANCOVA also…

Answer 27

1. Controls for covariance
2. Studies combinations of categorical and continuous variables, the covariate becomes the variable of interest RATHER than the one you control

Question 28

In a study where we test if technique has an impact on exam scores, but we want to account for the students current grade what is the covariate?

Answer 28

The current grade

Question 29

Assumptions of ANCOVA

Answer 29

1.Independent variablesshould becategorical variables.
2. Thedependent variableand covariate should be continuous variables(measured on aninterval scaleorratio scale.)
3. Make sureobservations are independent - don’t put people into more than one group.
4. Normality: the dependent variable should be roughlynormalfor each of category ofindependent variables.
5. Data (and regression slopes) should showhomogeneity of variance.
6. The covariate and dependent variable (at eachlevelof independent variable) should belinearly related.
7. Your data should behomoscedastic
8. The covariate and theindependent variableshouldn’t interact.In other words, there should be homogeneity of regression slopes.

Question 30

What do we partition in an ANCOVA?

Answer 30

Total variance into IV, DV, and covariate

Question 31

What do we partition in an ANOVA

Answer 31

Total variance into IV and DV

Question 32

Dummy Variables in an ANOVA

Answer 32

Binary value (0 or 1)
Control is always 0
One value will be 1 the other 0, they will not both be one