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# Statistics - Regression Analysis

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13.30 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)
153 observations
BirthRate is the dependent variable
p-values for the coefficients
Nvar LifeExp InfMort Density GDPCap Literate s Adj R2 R2
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

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 an assistant professor, 0 otherwise).
Interpret these results.

Variable Coefficient t p
Intercept &#8722;3,816,521 &#8722;29.4 .000
Year 1,948 29.8 .000
YearHire &#8722;826 &#8722;5.5 .000
Race &#8722;2,093 &#8722;4.3 .000
Rank &#8722;6,438 &#8722;22.3 .000
R2 = 0.811 R2
adj = 0.809 s = 3,318