POLI_399_tutorial_4

POLI 399 – Research Methods

Week Four

Causal Modelling

Today’s Agenda

What is a causal model? Elements of the causal model In-class Example

– Intervening Variable Model– Antecedent Variable Model– Source of Spuriousness Model

Establishing a Causal Relationship

Three conditions to establish causal relationship: (Jackson and Verberg, 442)

1. The variables must be associated (They vary together).

2. The variables must be in a plausible causal sequence (Believable ordering of variables).

3. The variables must not be spuriously connected (The relationship is not due to some third variable).

What is a Causal Model?

A causal model helps to clarify complex multivariate relationships by providing a visual representation of the relationships between variables. It also sets the stage for operationalization and the testing of hypotheses.

What is a Causal Model?

Your causal model should be built from your literature review. Existing research should be your guide.

You have to be able to defend the design of your causal model.

There should be a clear link between the literature review and the model you develop -- This should be made explicit in your research report.

Modelling Conservative Support in Canada

XX11

Support for less Support for less

government government

interventionintervention

YY11

Support for Steven HarperSupport for Steven Harper

++

XX33

gendergender

XX22

RegionRegion

+/-+/-

+/-+/-

Modelling Support for Private Health Care

XX11

XX22

Duration of Canadian citizenshipDuration of Canadian citizenship

EducationEducationYY

11

Support for private health careSupport for private health care

++

XX33

IncomeIncome

++

XX44

Possession of “Canadian values”Possession of “Canadian values”

++ ––

++

Things to include in your model

Identify the primary dependent and independent variables Label the variables (dependent=Y, independent=X) Draw causal arrows to indicate the direction of the relationship Insert symbols above the causal arrows: + for positive and –

for negative If either variable is measured at the nominal level, insert +/

– because the relationship does not have a direction If the literature has contradictory findings, label the

relationship with a ? Include all variables that could helps explain the relationship

between the independent and dependent variables (intervening variables) or that come before the it (antecedent)

Circle the variables that will be the focus of your research

In-class Example

Research question: What are the relationships between age, education and support for same sex marriage?

Background: We are conducting a research study on support for same sex marriage in Canada. Specifically, we are interested in whether one’s age and level of education affects one’s support for same sex marriage.

Modelling Support for Same Sex Marriage

YY11

Support for Same Sex MarriageSupport for Same Sex Marriage

XX11

AgeAge --

Initial Relationships

A negative sign can be interpreted like this:As a person’s age increases their support for same sex marriage decreases. (Positive X Negative = Negative)

Education LevelEducation Level

XX22

++

Modelling Support for Same Sex Marriage

Other research: However, as a result of our literature review we know that religiosity (the importance of religion in one’s life) also has an impact on support for same sex marriage.

The more importance that is placed on religion, the more likely that one is to believe that gays and lesbians should not be allowed to get married.

Modelling Support for Same Sex Marriage

YY11

Support for Same Sex MarriageSupport for Same Sex Marriage

XX33

ReligiosityReligiosity

AgeAge

--

XX11

--

Education LevelEducation Level

XX22 ++

A positive sign can be interpreted like this:The higher one’s level of education, the greater their support for same sex marriage. (Positive X Positive= Positive)

Modelling Support for Same Sex Marriage

The literature also says that there is a relationship between religiosity, age and education.

We have to edit our model to take this into account. In this case, religiosity acts as an intervening variable.

Modeling Support for Same Sex Marriage

YY11

Support for Same Sex MarriageSupport for Same Sex Marriage

XX33

ReligiosityReligiosity

AgeAge

--

XX11

++

Education LevelEducation Level

XX22

--

Religiosity acts as an intervening variable

Intervening Variable Model: Support for Same Sex Marriage

YY11

Support for Same Sex MarriageSupport for Same Sex Marriage

XX33

ReligiosityReligiosity

AgeAge

--

XX11

++

Education LevelEducation Level

XX22

--

By including religiosity as an intervening variable, I am hypothesizing that religiosity is most important because young people, who are very religious are still less likely to support same-sex marriage than then young people who are not religious.

Source of Spuriousness Model

While there is a relationship between X and Y, this relationship is non-causal because another variable influences both X and Y.

X and Y vary together because a third variable is influencing both of them. If we control for the third variable, there should no longer be a relationship between X and Y.

YYXX

S/SS/S

How to Create Models in MS Word

You can create your causal model directly in Microsoft Word. On the menu bar, click INSERT, PICTURE and AUTO SHAPES.

Here you will find the arrows we use in the model. Click lines and then the arrow. Right click to start and drag to where you want the arrow to end.

Use text boxes to add labels and the +/─ symbols to your models. Click INSERT, TEXT BOX and Horizontal. Enter your text. If you right click on the box, clicking FORMAT TEXT BOX allows you to change the width and colour of the box (selecting the colour ‘white’ removes the box)

Arrange the text boxes and the arrows appropriately on your page. How did I get the numbers beside the variables to look smaller (e.g.

X3). Highlight the number and right click on it. Select FONT and click the box beside SUBSCRIPT.

In-class Example

Use Word to create a causal model. Explain party support with two independent

variables. What might affect support for a political

party? Is the relationship positive or negative?

For Next Time...

Assignment #2 is available this Friday, October 10 on Blackboard.

The assignment is due October 17 before midnight.

Next week we will cover descriptive statistics and diagrams. Read chapter 6 of the SPSS guide and sections B5, B7, B8 in in Appendix A of Jackson and Verberg