Levene's test for equality of variances spss

Name:

SPSS Worksheet 1: (t-test)

Instructions: Lesson 24 Exercise File 1 is located at the end of the chapter under the heading Exercises in your Green and Salkind textbook. Complete the exercise and then complete the worksheet below by filling in the blanks and answering the questions.

H01: There is no significant difference in the amount of time it takes to eat a Big Mac meal between overweigh and normal weight individuals.

Assumptions

Outliers: Create a Box and Whisker plot for each group. Hint: Graph > Legacy > Boxplot > Simple. Insert the Box and Whisker plot below: Note: Look for extreme outliers.

Fill in the blanks:

Groups

Outliers (Item #); if none, enter n/a

Are there any outliers?

Overweight

n/a

no

Normal

n/a

no

Assumption of Normality: Run a normality test for each group. Hint: Begin by going to Analyze > Descriptive > Explore. See page 262. Insert the Tests of Normality table below:

Tests of Normality

Weight classification

Kolmogorov-Smirnova

Shapiro-Wilk

Statistic

df

Sig.

Statistic

df

Sig.

Time spent eating Big Mac specials in seconds

overweight

.237

10

.116

.907

10

.258

normal weight

.085

30

.200*

.982

30

.871

a. Lilliefors Significance Correction

*. This is a lower bound of the true significance.

Fill in the blanks:

Should you use a Shapiro-Wilks or Kolmogorov-Smirnov test? Why?

Answer: Since n<50 we use Shapiro -Wilks

Groups

Significance

Is the assumption of normality met?

Overweight

0.258

Yes

Normal

0.871

yes

Assumption of Equal Variance: Insert Levene's Test of Equality of Error Variancesa table(s) below:

Levene's Test of Equality of Error Variancesa

Dependent Variable:Time spent eating Big Mac specials in seconds

F

df1

df2

Sig.

2.745

1

38

.106

Tests the null hypothesis that the error variance of the dependent variable is equal across groups.

a. Design: Intercept + weight

Fill in the blanks:

Significance

Is the assumption of equal variance met?

0.106

yes

Results

Insert t-test for equality of Means table(s) below:

Independent Samples Test

Levene's Test for Equality of Variances

t-test for Equality of Means

F

Sig.

t

df

Sig. (2-tailed)

Mean Difference

Std. Error Difference

95% Confidence Interval of the Difference

Lower

Upper

Time spent eating Big Mac specials in seconds

Equal variances assumed

2.745

.106

-3.975

38

.000

-109.400

27.522

-165.116

-53.684

Equal variances not assumed

-5.397

30.828

.000

-109.400

20.272

-150.754

-68.046

Fill in the blanks:

Equal variances assumed

Value

df

38

t- statistic

-3.975

t- critical (Hint: See Appendix B in Warner)

2.745

p- value

0.000

Eta Squared (Hint: See formula)

1.45

Is the t-statistic greater than t-critical?

Hint: Use the absolute value.

Answer:

yes

Is the p-value less than .05?

Answer: yes

Should you reject or fail to reject the null?

Answer: reject

Is the effect size small, medium, or large? Hint: See Table 5.2 in Warner, p. 208.

Answer: small

Descriptive Statistics

Fill in the blanks:

Groups

M

SD

Overweight

589

42.615

Normal

698.4

82.949