Measures of Dispersion

• score = value but also observation

• variation/variability/dispersion/spread

• completes description of a distribution: mean/level, shape, and spread

• range - for ordinal and interval scale variables

• IQR (interquartile range)

• box plot

• variance (var.)

• standard deviation (s.d.)

 
 

• outliers: > 2 s.d. from mean

recommendations different from text:

• use as many measures of dispersion as are appropriate for your data

• IQV not very informative for ordinal variables

• be careful w/ percentage increases--also important to consider absolute percentage to interpret fully