Statistics Refresher
Scale Types
Nominal
Numbers as names
Ordinal
Ranks
Interval
Ranks and constant differences
Differences have meaning
Ratio
Interval and meaninful zero or origin
Ratios have meaning
Statistics for Distributions
Central Tendency
Mean:
Median
Mode
Variablility
Range: Maximum - Minimum
Variance in the population: 
where 
.
The sample estimator of the variance is: 
Standard deviation in the population:
The sample estimator of the standard deviation is: 
Shape
Normality
Skew
Kurtosis
Other types
(bimodal, uniform, etc.)