Chapter 12: Q2E (page 722)
Chapter 12: Q2E (page 722)
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Get started for freeComparing private and public college tuition. According to the Chronicle of Higher Education Almanac, 4-year private colleges charge, on average, five times as much for tuition and fees than 4-year public colleges. In order to estimate the true difference in the mean amounts charged for an academic year, random samples of 40 private colleges and 40 public colleges were contacted and questioned about their tuition structures.
Which of the procedures described in Chapter 8 could be used to estimate the difference in mean charges between private and public colleges?
Propose a regression model involving the qualitative independent variable type of college that could be used to investigate the difference between the means. Be sure to specify the coding scheme for the dummy variable in the model.
Explain how the regression model you developed in part b could be used to estimate the difference between the population means.
The first-order model was fit to n = 19 data points. A residual plot for the model is provided below. Is the need for a quadratic term in the model evident from the residual plot? Explain.
Question: Glass as a waste encapsulant. Because glass is not subject to radiation damage, encapsulation of waste in glass is considered to be one of the most promising solutions to the problem of low-level nuclear waste in the environment. However, chemical reactions may weaken the glass. This concern led to a study undertaken jointly by the Department of Materials Science and Engineering at the University of Florida and the U.S. Department of Energy to assess the utility of glass as a waste encapsulant. Corrosive chemical solutions (called corrosion baths) were prepared and applied directly to glass samples containing one of three types of waste (TDS-3A, FE, and AL); the chemical reactions were observed over time. A few of the key variables measured were
y = Amount of silicon (in parts per million) found in solution at end of experiment. (This is both a measure of the degree of breakdown in the glass and a proxy for the amount of radioactive species released into the environment.)
x1 = Temperature (°C) of the corrosion bath
x2 = 1 if waste type TDS-3A, 0 if not
x3 = 1 if waste type FE, 0 if not
(Waste type AL is the base level.) Suppose we want to model amount y of silicon as a function of temperature (x1) and type of waste (x2, x3).
a. Write a model that proposes parallel straight-line relationships between amount of silicon and temperature, one line for each of the three waste types.
b. Add terms for the interaction between temperature and waste type to the model of part a.
c. Refer to the model of part b. For each waste type, give the slope of the line relating amount of silicon to temperature.
e. Explain how you could test for the presence of temperature–waste type interaction.
Question: Consider the model:
where x1 is a quantitative variable and x2 and x3 are dummy variables describing a qualitative variable at three levels using the coding scheme
role="math" localid="1649846492724"
The resulting least squares prediction equation is
a. What is the response line (equation) for E(y) when x2 = x3 = 0? When x2 = 1 and x3 = 0? When x2 = 0 and x3 = 1?
b. What is the least squares prediction equation associated with level 1? Level 2? Level 3? Plot these on the same graph.
Question: Manipulating rates of return with stock splits. Some firms have been accused of using stock splits to manipulate their stock prices before being acquired by another firm. An article in Financial Management (Winter 2008) investigated the impact of stock splits on long-run stock performance for acquiring firms. A simplified version of the model fit by the researchers follows:
where
y = Firm’s 3-year buy-and-hold return rate (%)
x1 = {1 if stock split prior to acquisition, 0 if not}
x2 = {1 if firm’s discretionary accrual is high, 0 if discretionary accrual is low}
a. In terms of the β’s in the model, what is the mean buy and- hold return rate (BAR) for a firm with no stock split and a high discretionary accrual (DA)?
b. In terms of the β’s in the model, what is the mean BAR for a firm with no stock split and a low DA?
c. For firms with no stock split, find the difference between the mean BAR for firms with high and low DA. (Hint: Use your answers to parts a and b.)
d. Repeat part c for firms with a stock split.
e. Note that the differences, parts c and d, are not the same. Explain why this illustrates the notion of interaction between x1 and x2.
f. A test for H0: β3 = 0 yielded a p-value of 0.027. Using α = .05, interpret this result.
g. The researchers reported that the estimated values of both β2 and β3 are negative. Consequently, they conclude that “high-DA acquirers perform worse compared with low-DA acquirers. Moreover, the underperformance is even greater if high-DA acquirers have a stock split before acquisition.” Do you agree?
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