- 13.30 A A researcher used stepwise regression to create regression models to predict BirthRate (births
Problem #1 - 13.30 A
A researcher used stepwise regression to create regression models to predict BirthRate (births per 1,000) using five predictors: LifeExp (Life expectancy in years), InfMort (infant mortality rate), Density (population density per square kilometer), GDPCap (Gross Domestic Product per capita), and Literate (literacy percent). Interpret these results.
Regression Analysis – Stepwise Selection (best model of each size)
Observations
BirthRate is the dependent variable
| Nvar | LifeExp | InfMort | Density | GDPCap | Literate | S | Adj R \[^{2}\] | R \[^{2}\] |
| 1 | .0000 | 6.318 | .722 | .724 | ||||
| 2 | .0000 | .0000 | 5.334 | .802 | .805 | |||
| 3 | .0000 | .0242 | .0000 | 5.261 | .807 | .811 | ||
| 4 | .5764 | .0000 | .0311 | .0000 | 5.273 | .806 | .812 | |
| 5 | .5937 | .0000 | .6289 | .0440 | .0000 | 5.287 | .805 | .812 |
Problem #2 – 12.48
In the following regression, X= weekly pay, Y= income tax withheld, and n = 35 McDonald’s employees. (a) Write the fitted regression equation. (b). State the degrees of freedom for a two-tailed test for zero slope, find the critical value at α =.05 (c) What is your conclusion about the slope? (d) Interpret the 95 percent confidence limits for the slope. (e) Verify that F = \[{{t}^{2}}\] for the slope. (f) In your own words, describe the fit of this regression.
| R \[^{2}\] | 0.202 | |||||
| Std. Error | 6.816 | |||||
| N | 35 | |||||
| ANOVA table | ||||||
| Source | SS | Df | MS | F | p-value | |
| Regression | 387.6959 | 1 | 387.6959 | 8.35 | .0068 | |
| Residual | 1,533.0614 | 33 | 46.4564 | |||
| Total | 1,920.7573 | 34 | ||||
| Regression output | Confidence interval | |||||
| Variables | Coefficients | Std. error | T(df=33) | p-value | 95% lower | 95% upper |
| Intercept Slope | 1,743.57 | 288.82 | 6.037 | .0000 | 1,119.61 | 2,367.53 |
| Slope | -1.2163 | 0.4401 | -2.764 | .0161 | -2.1671 | -0.2656 |
Problem #3 – 12.50
In the following regression, X= total assets ($ billions), Y = total revenue ($ billions), and n = 64 large banks. (a) Write the fitted regression equation. (b) State the degrees of freedom for a two-tailed test for zero slope, find the critical value at α = .05 (c) What is your conclusion about the slope? (d) Interpret the 95 percent confidence limits for the slope. (e) Verify that F = t \[^{2}\] for the slope. (f) In your own words, describe the fit of this regression.
| R \[^{2}\] | 0.519 | |||||
| Std. Error | 6.977 | |||||
| N | 64 | |||||
| ANOVA table | ||||||
| Source | SS | Df | MS | F | p-value | |
| Regression | 3,260.0981 | 1 | 3,260.0981 | 66.97 | 1.90E-11 | |
| Residual | 3,018.3339 | 62 | 48.6828 | |||
| Total | 6.278.4320 | 63 | ||||
| Regression output | Confidence interval | |||||
| Variables | Coefficients | Std. error | T(df=33) | p-value | 95% lower | 95% upper |
| Intercept | 6.5763 | 1.9254 | 3.416 | .0011 | 2.7275 | 10.4252 |
| X1 | 0.0452 | 0.0055 | 8.183 | 1.90E-11 | 0.0342 | 0.0563 |
Problem #4 – 14.16
- Plot the data on U.S. general aviation shipments. (b) Describe the pattern and discuss possible causes. (c) Would a fitted trend be helpful? Explain. (d) Make a similar graph for 1992-2003 only. Would a fitted trend be helpful in making a prediction for 2004? (e) Fit a trend model of your choice to the 1992-2003 data. (f) Make a forecast for 2004, using either the fitted trend model or a judgment forecast. Why is it best to ignore earlier years in this data set?
| U.S. Manufactured General Aviation Shipments, 1966-2003 | |||||||
| Year | Planes | Year | Planes | Year | Planes | Year | Planes |
| 1966 | 15,587 | 1976 | 15,451 | 1986 | 1,495 | 1996 | 1,053 |
| 1967 | 13,484 | 1977 | 16,904 | 1987 | 1,085 | 1997 | 1,482 |
| 1968 | 13,556 | 1978 | 17,811 | 1988 | 1,143 | 1998 | 2,115 |
| 1969 | 12,407 | 1979 | 17,048 | 1989 | 1,535 | 1999 | 2,421 |
| 1970 | 7,277 | 1980 | 11,877 | 1990 | 1,134 | 2000 | 2,714 |
| 1971 | 7,346 | 1981 | 9,457 | 1991 | 1,021 | 2001 | 2,538 |
| 1972 | 9,774 | 1982 | 4,266 | 1992 | 856 | 2002 | 2,169 |
| 1973 | 13,646 | 1983 | 2,691 | 1993 | 870 | 2003 | 2,090 |
| 1974 | 14,166 | 1984 | 2,431 | 1994 | 881 | ||
| 1975 | 14,056 | 1985 | 2,029 | 1995 | 1,028 | ||
Problem #5 – 13.32
An expert witness in a case of alleged racial discrimination in a state university school of nursing introduced a regression of the determinants of Salary of each professor for each year during an 8-year period (n = 423) with the following results, with dependent variable Year (year in which the salary was observed) and predictors YearHire (year when the individual was hired), Race (1 if individual is black, 0 otherwise), and Rank (1 if individual is black, 0 otherwise), and Rank (1 if individual is an assistant professor, 0 otherwise). Interpret these results.
| Variable | Coefficient | T | P | |||
| Intercept | -3,816,521 | -29.4 | .000 | |||
| Year | 1,948 | 29.8 | .000 | |||
| YearHire | -826 | -5.5 | .000 | |||
| Race | -2,093 | -4.3 | .000 | |||
| Rank | -6,438 | -22.3 | .000 | |||
| \[\mathop{R}_{{}}^{2}=0.811\] | \[\mathop{R}_{adj}^{2}=0.809\] | S = 3,318 |
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