The Shape of Data

Distribution - the pattern of values in the data, showing their frequency of occurrence relative to each other.


There are some plots that can be useful for showing the distribution of data


Histogram is useful to show distribution of data

  • Bins: the intervals used in a histogram. The data must be separated into mutually exclusive and exhaustive bins
  • Cutpoints: the values that define the beginning and the end of the bins
  • Frequency: the count of the number of the data values in each bin
  • The peaks in the distribution are called modes

We can group distributions according to the number of modes they have:

  • unimodal - a distribution with one mode
  • bimodal - with 2 peaks
  • multimodal - more than 2 peaks

In R:

hist(..., breaks=10, ...) // histogram

Density Plots

Like a histogram, but smoothed



There are many distributions:

  • Uniform Distribution - equally spread without any mode
  • symmetric
    • the mean, median, and mode are all approximately the same.
    • dist-symmetric.png
  • assymetric
    • dist-asymetric.png
  • left-skewed
    • the longer tail on the left side
    • the mode is larger than the median which is larger than the mean
  • right-skewed
    • the longer tail on the right side
    • the mode is less than the median which is less the mean
    • dist-left-right.png
  • with gap
    • dist-gap.png

See Also