- The pth percentile is the value of the variable such that p% of the ordered data values are less than or equal to this value
- Empirical Cumulative Distribution Function (ECDF)
- all values <= percentile
- 510 = 78th percentile
- quartiles
- Q1 = 25th percentile
- Q2 = median = 50th percentile
- Q3 = 75th percentile
- five-number summary
- listing of minimum,Q1,median,Q3,maximum
- boxplot = a plot of the number summary
- jittered boxplot
- all sample points appear on the plot
- whiskers always stop at a value in the dataset
- cannot be bigger than 1.5xIQR
- values bigger than that are outliers
- large samplesize = more outliers, while the plot stays the same
- can lead to false conclusions
- keep in mind that ~1% will be outliers
- Interquartile Range (IQR)
- IQR = Q3 - Q1
- a descriptive measure of variability