Question 15.29

15.29 Smart shopping carts.

In Example 7.10 (pages 381-382) we compared spending by shoppers on a budget using a shopping cart equipped with or without real-time feedback. In Exercise 7.67 (page 397) we compared spending by shoppers not on a budget using a shopping cart equipped with or without real-time feedback. Let’s now perform a two-factor ANOVA of these data.

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  1. Construct a plot of the means and describe the main features of the plot.
  2. Analyze the data using a two-way ANOVA. Report the statistics, degrees of freedom, and -values. Because the are not equal, different software may give slightly different statistics and -values.
  3. Write a short summary of your findings.
  4. Describe the benefits of this analysis compared to the two tests previously performed.

15.29

(a) For those with real-time feedback, the average total cost for those not informed was only slightly larger than the average total cost of those informed, while for those without feedback, the not informed average was much larger than for those who were informed. Additionally, we can see an interaction effect. For those not informed, the lack of real-time feedback increased their spending, while for those who were informed, the lack of real-time feedback decreased their spending. (b) (c) The interaction term is significant as is the Informed term The Smartcart term is not significant Effects are interpreted as in part (a). (d) The two-factor ANOVA is better than two t tests because not only do we see the difference with and without feedback, we can also see the interaction effect where the lack of feedback increases spending for those not informed and decreases spending for those informed.