Research indicates that paying students to improve their grades simply does not

Question

Research indicates that paying students to improve their grades simply does not work (Fryer, 2011). However, paying students for specific tasks such as reading books, attending class, or doing homework does have a significant effect. Apparently, students on their own do not understand how to get good grades. If they are told exactly what to do, however, the incentives work. The following data represent a two-factor study attempting to replicate this result. a. Use a two-factor ANOVA with alpha =.05 to evaluate the significance of the main effects and the interaction. b. Calculate the eta^2 values to measure the effect size for the two main effects and the interaction. c. Describe the pattern of results. (How does paying for grades influence performance? How does paying for homework influence performance? Does the effect of paying for homework depend on whether you also pay for grades?)

Explanation / Answer

Result:

a).

Two factor ANOVA

Factor 2

Means:

Homework

No Homework

Garden

10.0

5.0

7.5

Factor 1

No Garden

9.0

4.0

6.5

9.5

4.5

7.0

ANOVA

Source of Variation

SS

df

MS

F

P-value

F crit

Garden

6.0000

1

6.0000

1.1538

0.2955

4.3512

Homework

150.0000

1

150.0000

28.8462

0.0000

4.3512

Interaction

0.0000

1

0.0000

0.0000

1.0000

4.3512

Within

104.0000

20

5.2000

Total

260.0000

23

Level of significance

0.05

Test for main effect garden, calculated F=1.1538 < critical value 4.35. The main effect is not significant.

Test for main effect Homework, calculated F=28.8462 > critical value 4.35. The main effect is significant.

Test for interaction effect garden, calculated F=0.0 < critical value 4.35. The interaction effect is not significant.

b).

effect size for Garden, 6/260=0.023

effect size for Homework, 150/260=0.5769

effect size for interaction, 0/260=0.00

c).

Paying for homework has a positive effect on grades. Paying for Garden has no effect on grades. Paying for homework does not depend on whether we pay for gardens.

Two factor ANOVA

Factor 2

Means:

Homework

No Homework

Garden

10.0

5.0

7.5

Factor 1

No Garden

9.0

4.0

6.5

9.5

4.5

7.0

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