class 4 - measurement
TRANSCRIPT
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Measurement Note: Chapter 4 workbook exercises dueTuesday, February 15
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Measurement
• Def: Systematic observation and representation by scores or
numerals, of the variables we have decided to investigate
(JRM)
• Conceptual definition vs. Operational Definition
• Concepts vs. Indicators
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MEASUREMENT
Examples• Hypothesis: The level of democracy in a country is negatively
related to the level of political violence
Key Question: How do we operationalize the dependent and
independent variables in this hypothesis?
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Operational Definitions
• Operationalize Democracy:
• Turnout – The percentage of eligible citizens voting in the last
national election
• Operationalize Political Violence:
• Riots – any act of spontaneous collective violence (rock throwing,vandalism, arson, sniping, beatings) involving 30 or more people
that can be interpreted as politically motivated
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Levels of Measurement
• Orderable (Ordinal, Interval, Ratio)
vs.
• Non-orderable Variables (Nominal)
• Orderable Variable: Values of an orderable variable represent
quantities of that variable, such that any value of a variable X
must be either >, <, or = to any other value of X
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Ordinal Variables
• Ordinal: Assume there exists a variable X with
values X1, X2, and X3, where X1 < X2 < X3 (i.e. it
is orderable).•
This variable is said to be measured at the ordinal level if it is notcertain that the quantity of X represented by |X1 - X2| is equal to
the quantity of X represented by |X2 - X3|
• Example: X=Olympic Performance,
• where 1=Bronze, 2=Silver, 3=Gold
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Ordinal Variables
X1 X2
X
X3
the quantity of X represented by |X1 - X2| is notknown to be equal to the quantity of X representedby |X2-X3|
Example: Olympic Performance(Bronze, Silver, Gold)
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Interval Variables
• Interval: Assume there exists a variable X withvalues X1, X2, and X3, where X1 < X2 < X3 (i.e. itis orderable).
• This variable is said to be measured at the intervallevel if we know that the quantity of X represented by|X1 - X2| IS equal to the quantity of X represented by|X2-X3|;
• AND the measurement scale does not contain at TRUE
zero
• Example: Temperature
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Interval Variables
X1
X2
X
X3
the quantity of X represented by |X1 - X2| IS equal to the quantity of X represented by |X2-X3|
Example: Temperature
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Ratio Variables
• Ratio: A variable measured at the ratio level is
simply an interval level variable with a "true"
zero (i.e. where a value of zero represents a
complete absence of that variable)
• Example: Prize money for a golf tournament (in thousands of
$)
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Nominal Variables
• Nominal – Classification of observations into a set of
categories that do not have direction (i.e. do not represent
quantities of that variable)
• Example: Race, where 1= White, 2=Black, 3=Asian, 4=NativeAmerican
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Other Types of Variables
• Dichotomous Variable:
• Variables that take on only two values
• Can be orderable or nominal
• Discrete Variable:
• Orderable variable that can take on limited values
• Examples:
• 1, 2, 3, 4….
• 1979, 1980, 1981…
•
Continuous Variable:• Orderable variable variable that can take on a limitless set of
values
• Example: decimals
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Examples
• Determine whether the following variables are (i) discrete or continuous,
• and (ii) measured at the nominal, ordinal, interval or ratio levels.
• Academic Department Size (number of faculty)
• Region of Nation (North, South, East, West)
• TV watching (avg. hours spent watching TV per week)
• Crime Rate (crimes per 100,000 population)
• Hometown (city of residence)
• Partisanship (% voting Republican by precinct)
• Partisanship (party that individual is registered as)
• Ideology (7-point scale from Extremely Liberal to Extremely Conservative)
•
Percentage of state population that is Hispanic• Year of birth
• Weight of contestant
• Size of drink (small, medium, large, biggie)
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Measurement Quality
• Measurement Error – Lack of correspondence between
observed indicator and underlying concept
• Validity
• Reliability
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Measurement Quality - Validity
• Validity - The extent to which a measurement procedure
measures what it intends to measure
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Measurement Quality - Validity
• Determine if the following indicators are valid measures of the
underlying concept
• Party registration (Dem, Rep or Ind) as a measure of political
ideology• Number of riots as a measure of political violence
• GPA as a measure of academic aptitude
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Assessing Validity
• Face validity – does the measure appear valid?
• Content validity – does the measure encompass
the entire domain of the concept?
• Construct validity – is this measure related to
other variables that would be suggested bytheory?
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Assessing Validity
• Content validity – does the measure encompass
the entire domain of the concept?
• Example: An individual’s ideology (liberal-conservative) as measured by the following
question:
• “Do you support a woman’s right to have an
abortion?”
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Assessing Validity
• Construct validity – is this measure related to
other variables that would be suggested by
theory?
• Example – GRE or LSAT scores
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Measurement Quality - Reliability
• Reliability – the extent to which a measuring instrument
consistently measures whatever it is that it is measuring
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Measurement Quality - Reliability
• Determine if the following measures are reliable
• Level of racial stereotyping (based on interviewer by phone)
• Gender of an individual (based on interviewer observation in
face-to-face survey)• Weight of an individual (on a scale) as a measure of ideology
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Improving Measurement
Quality• Creating multi-item measures
• Reduce errors in measurement that occur by using a single
variable
• Different types
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Original CPS Political Efficacy Index [agree-disagree]
• 1. People like me don't have any say about what the government does.
• 2. Sometimes politics and government seem so complicated that a personlike me can't really understand what's gong on.
•
3. Voting is the only way that people like me can have any say about howthe government runs things.
• 4. I don't think public officials care much what people like me think.
• 5. Generally speaking, those we elect to Congress in Washington lose
touch with the people pretty quickly.
• 6. Parties are only interested in people's votes but not in their opinions.
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Class Exercise…
Devise a measure of political ideology
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Example: Judicial Ideology