Problem Set 8: Multiple Regression

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Datasets for this assignment:

A random sample of 1,000 federal personnel records for March 1994:

• Download Dataset ‘OPM94’ (click “Save As”)

LOAD LIBRARIES

library(dplyr)
library(ggplot2)

DATA

Load OPM94.RData

# your work

MULTIPLE REGRESSION

Categorical (factor) level explanatory variable / multiple binary variables

Check the value of the patco variable using levels(opm94$patco) command:

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QUESTION 1:

What type is this variable? What values does it have?

Regress sal on patco:

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QUESTION 2:

a) What is the reference group?



b) Interpret the intercept:



c) Interpret the coefficient on `patcoClerical`:



d) Interpret the coefficient of `patcoProfessional`:

All Variable Types

Regress sal on minority and grade:

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QUESTION 3:

a) What is the reference group?



b) Interpret the intercept:



c) Interpret the coefficient on `minority`:


d) Interpret the coefficient on `grade`:

Regress sal on minority:

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QUESTION 4:

a) Interpret the intercept:



b) Interpret the coefficient on `minority`:



c) Why is the coefficient on `minority` different in this regression compared to the previous one (with `grade` included)?

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