# [POL242Y5] - Midterm Exam Guide - Comprehensive Notes for the exam (22 pages long!)

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Published on 7 Feb 2017

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POL242Y5

MIDTERM EXAM

STUDY GUIDE

Pol242 January 9, 2017 Multiple Regression

Multiple Regression

Just regression with more variables!

o Instead of one independent variable, two or more

Age causes income

But lots of things causes income; age, education, gender,

immigrant status – we are looking at it at the same time

Instead of line have plan going through it – different

dimensions

Interpreting Multiple Regression

Multiple slopes, one intercept

o Each has own p-value, confidence interval

Useful for controlling for other variables

Adjusted r squared (hoe closely the dots fit the line)

o If you add more variables the r squared goes up even

if it does not make sense so do not use r squared for

multiple regression

Calculate predicted value of Y by setting a value of all the

variables (Xs)

o Pick a spot on the line if x is this y is going to be…

Bivariate: if X is one higher, Y increases by (coefficient)

Multivariate: If X1, is one unit higher, and other Xs are the

same, Y increases by (coefficient)

The regression coefficient (slope) is the change in Y for a

one unit change in X holding the other variables constant

o For each one unit increase in IV, holding everything

else constant, what is increase in DV?

o For one year older, if education stays the same, what

is the increase in income?

Example

Hypothesis: Older people earn more money than younger

people

find more resources at oneclass.com

find more resources at oneclass.com

Theory: Older people get paid more BECAUSE their

bosses respect them more, and they get taken more

seriously

Pull apart age and experience

Interpreting Multiple Regression

Y=bX+a Income=Age + intercept

Y=2X+20 One unit increase in Age means

two unit increase in Income

Y=b1X1+b2X2+a Income= Experience +Age+

intercept

Y=1Xx+3X2+5 b1: one unit increase in Age means

a one unit increase in

Income…HOLDING Age THE SAME

b2: One unit increase in Experience

means a three unit increase in

Income…HOLDING Age THE SAME

Slope: If x changes by 1 unit y changes by for example y=2xt20

so increases by 2,

What is a one unit change?

Dependent variable has to be interval

Binary Variables

Only two possibilities

Binary variables are either 0 or 1

Can be nominal

Only for IV, not DV!!

Vote/not vote

Student/not student

Male/female

Always one unit increase for binary

Better to have ordinal do not turn it into a binary (need

more or less of it)

Regression with a binary variable

Y=bX+a Test Mark = Hours studying + intercept

Y=3X+40 One unit increase in studying means a 3

unit increase in Test Mark

find more resources at oneclass.com

find more resources at oneclass.com