POLS 7000X Statistics in political science Class 1 Brooklyn College – CUNY Shang E. Ha
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Transcript of POLS 7000X Statistics in political science Class 1 Brooklyn College – CUNY Shang E. Ha
POLS 7000XSTATISTICS IN POLITICAL SCIENCE
CLASS 1BROOKLYN COLLEGE – CUNYSHANG E. HA
Leon-Guerrero and Frankfort-Nachmias, Essentials of Statistics for a Diverse Society, Chapter 1
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society© 2012 SAGE Publications
Empirical Research What is Empirical Research? Research based on information that can be verified by
using our direct experience.
A research… 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
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): 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: 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 AnalysisThe level of social life on which social
scientists focus (individuals, groups). Examples:
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)
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 Dependent
The variable to be explained (the “effect”). Should be identified in our research question
Why are some people favorable to homosexuality? Dependent variable – attitudes toward homosexuality
Independent The variable expected to account for (the “cause”
of) the dependent variable. Should be identified in our hypothesis
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 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)
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. The dependent variable is always the property you are trying to explain; it is always the object of the research.
2. The independent variable usually occurs earlier in time than the dependent variables.
3. 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 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
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:– Dependent variable:
• Identify other independent variables
Gender
• Are the causal arguments sound?
– e.g. Does party id affect abortion views or vice versa?
Church attendance
Age
Attitudes toward abortion
Religious affiliation (Catholic, Jewish, Methodist, Islamic…)Political party identification
Example 1
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society© 2012 SAGE Publications
Hypothesis: The number of books read to a child per day positively affects a child’s word recognition.
• Identify the IV and DV
• Identify other independent variables
• Are the causal arguments sound?
– independent variable:
– dependent variable:
Gender
– 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.
Number of books read
Older siblings
Word recognition
Health status Birth order
Example 2
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society© 2012 SAGE Publications
Collecting Data
Asking the Research Question
Formulating the
Hypotheses
Evaluating the
Hypotheses
Analyzing Data
Develop a research design
Contribute new evidence to literature and begin again
THEORY
Examine a social relationship, study the relevant literature
Collecting Data
Leon-Guerrero/Frankfort-Nachmias: Essentials of Social Statistics for a Diverse Society© 2012 SAGE Publications
Collecting DataResearchers 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 MeasurementNot 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:
NominalOrdinalInterval-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 ClassUpper ClassMiddle ClassWorking 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: AgeIncomeSAT 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 No Ordinal Yes Yes 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: the number children per family
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.