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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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Why does the experiment wise error rate of a multiplecomparisons procedure differ from the significance level for each comparison (assuming the experiment has more than two treatments)?
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’s 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’s 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.
Mixed gender decision-making groups. In business, a group of executives is often assigned to make key decisions. The American Journal of Political Science (April 2014) published a study on a woman’s impact on mixed-gender deliberating groups. The researchers randomly assigned subjects to one of several 5-member decision-making groups. The
groups’ gender composition varied as follows: 0 females, 1 female, 2 females, 3 females, 4 females, or 5 females. Each group was then randomly assigned to utilize one of two types of decision rules: unanimous or majority rule. Ten groups were created for each of the 6 * 2 = 12 combinations of gender composition and decision rule. One variable
of interest, measured for each group, was the number of words spoken by women on a certain topic per 1,000 total words spoken during the deliberations.
a. Why is this experiment considered a designed study?
b. Identify the experimental unit and dependent variable in this study.
c. Identify the factors for this study. Give the levels of each factor.
d. How many treatments are in this study? List them.
What is the difference between a one-way ANOVA and atwo-way ANOVA?
Contingent valuation of homes in contaminated areas. Contingent valuation (CV) is a method of estimating property values that uses survey responses from potential homeowners. CV surveys were employed to determine the impact of contamination on property values in the Journal of Real Estate Research (Vol. 27, 2005). Homeowners were randomly selected from each of seven states—Kentucky, Pennsylvania, Ohio, Alabama, Illinois, South Carolina, and Texas. Each homeowner was asked to estimate the property value of a home located in an area contaminated by petroleum leaking from underground storage tanks (LUST). The dependent variable of interest was the LUST discount percentage (i.e., the difference between the current home value and estimated LUST value as a percentage). The researchers were interested in comparing the mean LUST discount percentages across the seven states.
a. Give the null and alternative hypotheses of interest to the researchers.
b. An ANOVA summary table is shown below. Use the information provided to conduct the hypothesis test, part a. Use \(\alpha = 0.10\).
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