Review.

POL 242 – 2008-09

Strong Correlation. Positive or Negative?

NU

YT

NW

AB

NL NB

MB

SK

QC

BCPE

NS

ON

010

2030

40%

Rev

enue

from

inco

me

tax

0 10 20 30% Revenue from consumption tax

Correlation: Sources of Provincial Revenues

Correlations - Views0

24

68

10S

ame

Se

x M

arri

age

0 2 4 6 8 10Abortion

Views on Abortion and Same Sex Marriage

02

46

810

Cu

ttin

g T

axe

s

0 2 4 6 8 10Abortion

Views on Abortion and Cutting Taxes

Adding a 3rd (& 4th & 5th) Variable More than one independent variable. How

can we characterize the relationship between these independent variables and the dependent variable. Additive Antecedent Intervening

Original Relationship Can Change Did the relationship between X and Y

change at different levels of the new variable? Did the relationship get weaker? stronger? Did the sign change or stay the same?

Focus on the relationship between X & Y, not on how the new variable affects the independent variable.

Control Tables

Look at a bivariate relationship at different levels of the [new] control variable.

Observe appropriate measures of association How can you gauge if there is elaboration?

What to do if there is elaboration If the relationship between x and y

dramatically changes at different values of z, then you want to create an interaction term.

Need a new line with a different slope for those values of z.

Remember to include the original variables in the equation as independent variables.

Interpreting Interactions

Two Dummies EX: Immigrant and univ graduate.

Three coefficients Immigrant Univ Graduate Immigrant * Univ Graduate (Interaction)

Immigrant= immigrants w/o univ. diploma Univ Grad = non-immigrant graduates Interaction = immigrants WITH diploma

Interpreting Interactions - II

Dummy + Ordinal, Ex: Race (white = 1) and Political Interest (ordinal 5 pt scale)

Three coefficients White = effect of being white with no political

interest on DV Political Interest = effect of political interest on DV

for non-whites only Interaction = Effect of political interest on DV for

whites only.

Regression – To Do

Need to run a regression Interpret that regression

B! Significance

Could there be a multicollinearity problem? Tolerance / VIF

Beta R-squared

Advanced Regression - To Do Recode variables

Create a dummy variable Rules of creating dummies Interpretation of dummies

Create an interaction term Interpretation of all terms in equation

Run a regression on sub-sets of sample

When should you not run a Regression OLS = Ordinary Least Squares Regression Best for interval dependent variables or

ordinal variables with at least five different categories. Also imposes other restrictions about distribution

of variable and the error term You can run a logit regression on a

dichotomous dependent variable.

Logit Rules

You can run a logit regression on a dichotomous dependent variable. But you cannot directly interpret the coefficients. You can tell whether the effect is negative or

positive, and whether the effect is statistically significant.

Remember how to see if the model did a good job of predicting the actual results.

Final Product

Evaluate your hypothesis or hypotheses. If evidence is consistent with your hypothesis,

reject your null hypothesis. Make your point(s) very clearly. Do your readers know everything they need

to know? And remember that they may not be interested in

EVERYTHING.

Details

Everyone come to class next week (12:15 papers to the office will be marked LATE). If you are not taking test in-class, you should be in

location with internet access. Everyone should fill out an evaluation form.

TAs Professors

Papers go to Turnitin.com

Details – Open Book Section

Start on internet with Webstats. Can reference class materials (labs, lectures), but your time is limited.

May not converse with others (talk, IM, etc) or consult other people’s analyses.

Can bring disk or USB memory key to save Word document for your answers (can also save to My Documents)

At end, email answers YOURSELF and to pol242y@canada.com and upload to Blackboard.

Second Half – Closed Book

28 questions (1/2 value of test) is closed book. NO INTERNET.

Multiple choice, true/false, fill in the blank and some short answers.

Recommended: 45 minutes Difficulty: should be similar to labs and

worksheets. If you are well-prepared, I expect you will do well.