t-tests and one way anova (presentation 3) adv stat

8/11/2019 T-tests and One Way ANOVA (Presentation 3) Adv Stat

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1

T-Test for Independent

Groups



2

Aim



3

Checklist of Requirements



Assumptions The sampling distribution of differences

between means is normally distributed.

Homogeneity of variance.



5

Example



SPSS Output



Results and

Interpretation



Results and Interpretation Levene’s Test for Equality of Variances tests the

hypothesis that the two population variances are equal.

In this example, the Levene statistic is F = 0.087, and the

corresponding level of significance is large (i.e., p> .05).

Thus, the assumption of homogeneity of variance has

not been violated, and the Equal variances assumed t-test statistic can be used for evaluating the null

hypothesis of equality of means. If the significance level

of the Levene statistic is small (i.e., p< .05), the

assumption that the populationvariances are equal isrejected and the Equal variances not assumedt-test

statistic should be used.



Results and Interpretation

The result from the analysis indicates thatthere is a significant difference between the

male and female samples in the number of

words correctly recalled, t(df = 18) = – 3.02, p <

.01. The mean values indicate that femalescorrectly recalled significantly more words (M

= 22.10) than males (M = 17.70).



Hands-on Exercise 2:

Use dataset Coronary artery data.sav andanswer the following question:

Is there a significant difference in thetreadmill time of the subjects during their

daily exercise when they are grouped

according to their health condition?



PAIRED-SAMPLES

T-TEST



Aim



19


• In any one analysis, there must beonly two sets of data.

• The two sets of data must be

obtained from (1) the same subjectsor (2) from two matched groups of

subjects.



20

Assumptions

The sampling distribution of themeans should be normally

distributed.

The sampling distribution of thedifference scores should be normally

distributed.



Example



Windows Method



23



24

SPSS Output



25


The result from the analysis indicates thatthere is a significant difference in the amount

of food eaten before and after drug X was

ingested, t(df = 9) = 5.08, p < .01. The mean

values indicate that significantly less food wasconsumed after ingestion of drug X (M =

124.00) than before (M = 177.00).



One-Way Analysis of Variance

with Post Hoc Comparisons

594594594594 N =

SOCIALCAMPUSTEACHGEDUCAT

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4

4

4

4

3



27

Aim



28




29

Assumptions



30

Example



31

Windows Method



36

SPSS Output



38


The results from the analysis indicatethat the intensity of the electric shockhas a significant effect on the time

taken to solve the problems, F(2,15) =40.13, p< .001. The mean values forthe three shock levels indicate that asthe shock level increased (from low tomedium to high), so did the time takento solve the problems (low: M = 17.17;medium: M = 22.17; high: M = 42.17).



Post Hoc Comparisons



Workshop 1:

Using the Employee data file, is there asignificant difference in the current salary ofthe employees when they are groupedaccording to employment category and

educational level?



Workshop 2:Using the 1991 US General Social Survey data, is there a

significant difference in the general happiness and lifeexcitement perception of the respondents when theyare grouped according to :

• Race, (GH=S, LE=NS), white race happier than black

• Regional location, (NS)

• Number of children, (NS)

• Occupational category (S), managerial vs gen labor,

and• Highest year of school completed?

t-tests and one way anova (presentation 3) adv stat

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