POL 51 Lecture 7: Lecture 7

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7 Feb 2017
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FEB 6
Lecture 7
Types of Variables
- Categorical
- Nominal values
- Can’t make a ranking w/values
- Just different from each other
- Ex. religious affiliation, city of residence
- Ordinal
- Values that can be categorized (by rank/order)
- Distances between values is not equal
- Ex. feeling thermometers, party identification
- Continuous
- Distances between values are known and has meaning
- Equal-unit spacing
- Distances between values is equal and meaningful
- Ex. age, time
Notation
- n = the # of cases/observations
- Y-bar or μ = mean
- σ / SD = standard deviation
- σ² = variance
- Typically denote a variable as Y when doing descriptive statistics
- Doesn’t matter if variable is our DV or IV
Descriptive Statistics
- Need ways to describe data
- Learn about the distribution
- Ex. what do the set of values for the variable look like?
- Central Tendency tells us about the “typical value” of a variable at the center of the distribution
- Mode
- “Modal response”
- Most common value, most “popular”
- Mostly used for describing central tendency of categorical variables
- Mean (Y-bar or μ)
- “Average” or “expected value” from a distribution
- Guesses the value of a variable from a case
- The best choice if there is little info
- Can be affected by outliers
- Sum of Y values divided by n
- Denoted as Y-bar or μ
- Median
- Middle/center of the distribution
- The value at the 50th percentile
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