Measurement and Variables

May 14 , 2008

Ivan

Katchanovski, Ph.D.

POL 242Y-Y

Outline• How to design a research project• Research questions and research hypotheses• Units of analysis• Concepts of political science• Variables• Levels of measurement– Nominal– Ordinal– Interval/ratio

• Measurement Reliability and Validity

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How to Design a Research Project• Define the purpose of your project

• Specify exact meanings for the concepts you want to study

• Specify a research question or a research hypothesis

• Choose a research method

• Decide how to measure the results

• Decide whom or what to study

• Collect empirical data

• Process the data

• Analyze the data

• Report your findings

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Research Questions and Research Hypotheses

• Research question: a testable question about empirical reality that follows from a more general proposition (a theory)– Is the level of economic development related to democracy

– Do women and men vote for different political parties

• Research Hypothesis: testable expectation about empirical reality that follows from a more general proposition (a theory)– The level of economic development has a positive effect on

democracy

– Men are significantly more likely than women to vote for the Conservative Party of Canada

• Research is designed to answer research questions or test hypotheses

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Units of Analysis• Individual level: – Individuals, members of the parliament, individual

laws, students in POL242 class – Typical in surveys: individual respondents

• Aggregate level:– Countries, provinces, classes at U of T

• Ecological fallacy: assuming something learned about an aggregate level phenomenon says something about the individuals in the aggregate unit– High income provinces vote for Liberals does not

necessarily mean that rich people vote for Liberals

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Concepts

• Concepts: ideas or constructs that represent real world phenomena – Democracy

– Party affiliation

– Social capital

– Tolerance

– Political conservatism

– Social liberalism

– Globalization

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Variables• Provide measurement of concepts• Contain different values• Examples: • Democracy variable can have the following values:

1. Democratic country2. Non-democratic country

• Political party affiliation in Canada variable can have the following values:1. Conservative2. Liberal3. NDP4. Other party

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Levels of Measurement

In Theory

• Nominal

• Ordinal

• Interval/ratio

In Practice

• Ordinal variables are often treated as similar to interval/ratio variables

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Nominal Measure (Variable)

• Nominal : A level of measurement describing a variable that has values that cannot be ranked in contrast to other types of variables

• Examples of nominal measures:– Gender: Women and men cannot be ranked

– Political party affiliation: Political parties cannot be ranked

– Country: Countries cannot be ranked

Ordinal Measure (Variable)• Ordinal : A level of measurement describing a

variable with values we can rank-order along some dimension but cannot find the average value (the mean)

• Examples:– education as composed of the following values: high

school, university, post-graduate

– socioeconomic status as composed of the following values: high, medium, low

– religiosity as composed of the following values: very high, moderately high, moderately low, very low

Interval/Ratio Measures (Variable)

• Interval/Ratio: A level of measurement describing a variable whose values are rank-ordered and have equal distances between adjacent values

• Examples:– Age (years)

– Income

– Percentage of vote for a presidential candidate

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Question

• Which of the following are examples of nominal variables?

A. Religious affiliation (Catholic, Jewish, Muslim, Protestant, Other)

B. Race (Asian, Black, White, Other)C. GDP per capita ($)D. Education (years)E. Defence spending as % of government budgetF. Socio-economic class (lower, working, middle,

upper) G. Grade (pass, fail)

Measurement Reliability and Validity

• Reliability: – Quality of measurement method that suggests that

the same data would have been collected each time in repeated observations of the same phenomenon

• Validity– A term describing a measure that accurately reflects

the concept it is intended to measure

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