Heyman and Ariely (2004) were interested in whether effort and willingness to help were affected by the form and amount of payment offered in return for effort. They predicted that when money was used as payment, in what is called a money market, effort would increase as a function of payment level. On the other hand, if effort were performed out of altruism, in what is called a social market, the level of effort would be consistently high and unaffected by level of payment. In one of their studies, college students were asked to estimate another student’s willingness to help load a sofa into a van in return for a cash payment or candy of equivalent value. Willingness to help was assessed using an 11-point scale ranging from “Not at all likely to help” to “Will help for sure.” Data are presented here to re-create some of their findings.

Cash payment, low amount of $0.50: 4, 5, 6, 4

Cash payment, moderate amount of $5.00: 7, 8, 8, 7

Candy payment, low amount valued at $0.50: 6, 5, 7, 7

Candy payment, moderate amount valued at $5.00: 8, 6, 5, 5

a. What are the independent variables and their levels?

b. What is the dependent variable?

c. Draw a table that lists the cells of the study design. Include the cell and marginal means.

d. Create a bar graph.

e. Using this graph and the table of cell means, describe what effects you see in the pattern of the data.

f. Write the null and research hypotheses.

g. Complete all of the calculations and construct a full source table for these data.

h. Determine the critical value for each effect at a p level of 0.05.

i. Make your decisions. Is there a significant interaction? If yes, describe it in words and indicate whether it is a qualitative or a quantitative interaction. Explain.

j. Compute the effect sizes, R², for the main effects and interaction. Using Cohen’s conventions, interpret the effect-size values.