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Chapter 9: Q3E (page 522)
What is the difference between an observational experiment and a designed experiment?
In a designed experiment, the researcher controls the treatment specifications. While in the observational experiment, he observes the treatments, but he cannot control the treatments.
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What are the treatments for a designed experiment that uses one qualitative factor with four levels鈥擜, B, C, and D?
Identifying the type of experiment. Brief descriptions of a number of experiments are given next. Determine whether each is observational or designed and explain your reasoning.
a. An economist obtains the unemployment rate and gross state product for a sample of states over the past 10 years, with the objective of examining the relationship between the unemployment rate and the gross state product by census region.
b. A manager in a paper production facility installs one of three incentive programs in each of nine plants to determine the effect of each program on productivity.
c. A marketer of personal computers runs ads in each of four national publications for one quarter and keeps track of the number of sales that are attributable to each publication鈥檚 ad.
d. An electric utility engages a consultant to monitor the discharge from its smokestack on a monthly basis over a 1-year period to relate the level of sulfur dioxide in the discharge to the load on the facility鈥檚 generators.
e. Intrastate trucking rates are compared before and after governmental deregulation of prices changed, with the comparison also taking into account distance of haul, goods hauled, and the price of diesel fuel.
Value perceptions of consumers (cont鈥檇). Refer to Exercise 9.10. In addition to the factor, Type of advertisement
(within-store price promotion and between-store price promotion), the researchers also investigated the impact of a second factor鈥擫ocation where ad is read (at home or in the store). About half of the consumers who
were assigned to the within-store price promotion read the ad at home, and the other half read the ad in the store. Similarly, about half of the consumers who were assigned to the between-store price promotion read the ad at home, and the other half read the ad in the store. In this second
experiment, the goal was to compare the average discount values of the groups of consumers created by combining Type of advertisement with Location.
a. How many treatments are involved in this experiment?
b. Identify the treatments.
Corporate sustainability and firm characteristics. Refer to the Business and Society (March 2011) study on how firm size and firm type impact corporate sustainability behaviors, Exercise 1.28 (p. 51). Certified Public Accountants (CPAs) were surveyed on their firms鈥� likelihood of reporting sustainability policies (measured as a probability between 0 and 1). The CPAs were divided into four groups depending on firm size (large or small) and firm type (public or private): large/public, large/private, small/ public, and small/private. One goal of the analysis was to determine whether the mean likelihood of reporting sustainability policies differs depending on firm size and firm type. Identify each of the following elements for this study:
a. Experimental units
b. Response variable
c. Factor(s)
d. Factor levels
e. Treatments
Robots trained to behave like ants. Robotic researchers investigated whether robots could be trained to behave like ants in an ant colony (Nature, August 2000). Robots were trained and randomly assigned to 鈥渃olonies鈥� (i.e., groups) consisting of 3, 6, 9, or 12 robots. The robots were assigned the task of foraging for 鈥渇ood鈥� and to recruit another robot when they identified a resource-rich area. One goal of the experiment was to compare the mean energy expended (per robot) of the four different colony sizes.
a. What type of experimental design was employed?
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