Download Identify other independent variables

POLS 7000X
STATISTICS IN POLITICAL SCIENCE
CLASS 1
BROOKLYN COLLEGE – CUNY
SHANG E. HA
Leon-Guerrero and Frankfort-Nachmias,
Essentials of Statistics for a Diverse Society, Chapter 1
Empirical Research

What is Empirical Research?

Research based on information that can be verified by using
our direct experience.

A research…
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That poses a question
That constructs hypotheses (i.e., potential answers)
That creates, gathers, and analyzes data
That tests hypotheses – correct or wrong?
That cumulates knowledge
Not only in political science but also in any other social science
disciplines
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Asking a Research Question
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To answer research questions we cannot rely on speculation,
moral judgment, or subjective preference
Instead, we create a set of potential answers (i.e., hypotheses)
and see whether data support our hypotheses by carefully
analyzing them
Empirical (a “Why” question):
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Why do some people commit suicide (and others don’t)?
Why are some individuals favorable to homosexuality (and
others are not)?
Why do some people vote in the mayoral elections (and others
don’t)?
Not Empirical:
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Is racial equality good for society?
Should death penalty be abolished?
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Units of Analysis
The level of social life on which social scientists
focus (individuals, groups). Examples:
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Individual as unit of analysis:
 Why are some people politically liberal while
others are conservative?
City as unit of analysis:
 Why is crime rate higher in some cities than others?
Country as unit of analysis:
 What determines income inequality across different
countries?
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Formulating the Hypotheses

Hypotheses:
Tentative answers to research questions (subject to
empirical verification)
 A statement of a relationship between
characteristics that vary (variables)
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Variable:
A property of people or objects that takes on two
or more values
 Must include categories that are both exhaustive
and mutually exclusive
 Examples: Social class, age, gender, income

Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Types of Variables
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Dependent
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The variable to be explained (the “effect”).
Should be identified in our research question
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Why are some people favorable to homosexuality?
Dependent variable – attitudes toward homosexuality
Independent
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The variable expected to account for (the “cause” of)
the dependent variable.
Should be identified in our hypothesis
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The more educated are more likely to harbor favorable
attitudes toward homosexuality
Independent variable – level of education
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
The Role of Theory


A theory is an explanation of the
relationship between two or more
observable attributes of individuals or
groups.
Social scientists use theory to attempt to
establish a link between what we observe
(the data) and our understanding of why
certain phenomena are related to each
other in a particular way.
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Hypothesis: An Example
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Research Question: What determines white Americans’ attitudes
toward immigrants from Latin American countries?
Hypothesis: White Americans who live in an area populated by a
significant proportion of immigrants are more likely to harbor
favorable attitudes toward them than those who live in another area
where few immigrants reside
Theory: Contact Theory (contact makes friends)

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Dependent variable: attitudes toward immigrants (favorable – hostile)
Independent variable: residential segregation (high: no immigrants –
low: many immigrants)
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Cause and Effect Relationships
Cause and effect relationships between
variables are not easy to infer in the social
sciences. Causal relationships must meet
three criteria:
1. The cause has to precede the effect in time
2. There has to be an empirical relationship
between the cause and effect
3. This relationship cannot be explained by
other factors
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Guidelines for Independent and
Dependent Variables
1.
2.
3.
The dependent variable is always the
property you are trying to explain; it is
always the object of the research.
The independent variable usually occurs
earlier in time than the dependent
variables.
The independent variable is often seen as
influencing, directly or indirectly, the
dependent variable.
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
One Hypothesis, Many Hypotheses
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Social phenomena are complex
Most of the social phenomena require researchers to assess the
effects of several independent variables on one dependent
variable
One independent variable usually explains only a certain
amount of the change in the values observed in the dependent
variable; hence, additional independent variables have to be
introduced in order to explain more of that variation.
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Example 1
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•
Hypothesis: People who attend church regularly
are more likely to oppose abortion than people
who do not attend church regularly.
Identify the IV and DV
– Independent variable:
Church attendance
– Dependent variable:
Attitudes toward abortion
Identify other independent variables
Gender
Age
Religious affiliation (Catholic, Jewish, Methodist, Islamic…)
Political party identification
•
Are the causal arguments sound?
– e.g. Does party id affect abortion views or vice versa?
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Example 2
Hypothesis: The number of books read
to a child per day positively affects a
child’s word recognition.
• Identify the IV and DV
– independent variable:
– dependent variable:
Number of books read
Word recognition
• Identify other independent variables
Older siblings
Gender
Birth order
Health status
• Are the causal arguments sound?
– Most likely. It is hard to construct an argument where a
36 month old child affects the number of books her/his
parent reads to her/him.
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Collecting Data
Asking the
Research
Question
Contribute new
evidence to
literature and
begin again
Evaluating the
Hypotheses
Examine a social relationship,
study the relevant literature
THEORY
Analyzing
Data
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Formulating
the
Hypotheses
Develop a
research
design
Collecting
Data
Collecting Data
Researchers must decide three things:
 How
to measure the variables of interest
 How to select the cases for the research
 What kind of data collection techniques
to use
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Levels of Measurement
Not every statistical operation can be used
with every variable. The type of statistical
operations we employ will depend on how
our variables are measured.
Variables are measured in three ways:
Nominal
Ordinal
Interval-Ratio
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Nominal Level of Measurement
Numbers or other symbols are assigned to a
set of categories for the purpose of naming,
labeling, or classifying the observations.

Examples:
Political Party (Democrat, Republican,
Independent)
Religion (Catholic, Jewish, Muslim, Protestant)
Race (African American, Latino, Native American)
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Ordinal Level of Measurement
Nominal variables that can be ranked from
low to high.
Example: Social Class
Upper Class
Middle Class
Working Class
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Interval-Ratio Level of Measurement
Variables where measurements for all cases
are expressed in the same units. (Variables
with a natural zero point, such as height and
weight, are called ratio variables.)
Examples:
Age
Income
SAT scores
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Cumulative Property of Levels of
Measurement
Variables that can be measured at the interval-ratio
level of measurement can also be measured at the
ordinal and nominal levels.
However, variables that are measured at the nominal
and ordinal levels can’t be measured at higher levels.
Level
Different or
Equivalent
Higher or
Lower
How Much
Higher
Nominal
Yes
No
Ordinal
Yes
Yes
No
No
Interval-ratio
Yes
Yes
Yes
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Discrete and Continuous Variables

Discrete variables: variables that have
a minimum-sized unit of measurement,
which cannot be sub-divided
 Example:
family

the number children per
Continuous variables: variables that,
in theory, can take on all possible
numerical values in a given interval
 Example:
length
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications
Analyzing Data:
Descriptive and Inferential Statistics
• Population: The total set of individuals,
objects, groups, or events in which the
researcher is interested.
• Sample: A relatively small subset selected from
a population.
• Descriptive statistics: Procedures that help us
organize and describe data collected from
either a sample or a population.
• Inferential statistics: The logic and procedures
concerned with making predictions or
inferences about a population from
observations and analyses of a sample.
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society
© 2012 SAGE Publications