Chapters 14-16 Quantitative Data Analysis Flashcards
Three Common Arguments and Claims in Quantitative Political Science
Descriptive claims - %
Claims of group differences
Claims of relationships between variables
Descriptive data helps us understand ____ variable(s).
One
Two Types of Basic Descriptive Statistics
Measures of central tendency
Measures of dispersion/variation
Selection of Univariate Stats/Levels of Measurement
Nominal
- central tendency is found through modes
- dispersion is found through variation ratio
Ordinal
- central tendency is found through mode and median
- dispersion is found through variation ratio and range
Interval
- Central tendency is found through mode, median and mean
- Dispersion is found through variation ratio, range, and standard deviation
Three Possible Measures of Central Tendency
Mode - that which occurs most frequently
Median - the sample median is the middle value when in order to increasing magnitude
Mean - average
Pros and Cons of the three Measures of Central Tendency
Mode cons: - susceptible to categorical construction (green and not green vs. green, ndp, lib, etc.) - doesn't use all data Mode pro: - can use with nominal measures Median con: - does not use precise values Median Pro: - stable, not affected by extreme values Mean pro: - uses precise values Mean con: - skewed by extreme
Statistical Distribution and Measures of Central Tendency
If stats are normally distributed (in a nice curve), then all three will be the same
If not distributed nicely, different central tendencies will pull data in different directions
3 Measures of Dispersion, and why we need it
Standard Deviation
Variation Ratio
Range
Because central tendency doesn’t give us all the information!
Deviation and Standard Deviation
- how far an individual score is from the mean
- standard deviation is the average deviation
- effected significantly by outliers (like all means) and sample size
Mean is appropriate to use when…
The standard deviation is minimal.
Variation Ratio
The number of cases that aren’t in the modal category.
High ratio means data are more dispersed.
Range
- Difference between highest and lowest score
- Can’t be used for nominal obvi
If there is an even number of cases and the two middle values are different, the median becomes…
The mean of the two middle numbers.
Positive and Negative Skew
Negative skew (low extremes) Positive skew (high extremes) Too many make mean a bad central tendency to use.
Is 80/100 cases are in the modal category, the variation ratio is…
0.2
So small.
Null Hypothesis
Mean of the control = mean of the treatment group
Alternative Hypothesis
Mean of the control group isn’t equal to that of the treatment group
Type 1 Error
False positive
Type 2 Error
False negative
Inferential Statistics
Stats which test the probability that sample statistics are reasonable estimates of population parameters.
5 Steps of Hypothesis Testing
- Formulate Null and Alternative
- Select a confidence level
- Calculate the appropriate inferential statistic
- Using the table for the test statistic, find the critical value (expected value) at the selected confidence level.
- If the calculated statistic equals or exceeds the critical value, reject the null.