Dispersion of samples in a data set

  If the samples of a data set are grouped close to the mean, the
  variance and standard deviation values will be close to 0.

  For example, consider some test scores from two groups of students:

    Group A = { 1, 2, 3, 4, 4, 4, 5, 7, 7, 7, 8, 10, 11, 11 }

    Group B = { 3, 4, 5, 5, 6, 7, 7, 7, 7, 9 }

  The mean score for the two groups is the same (6), but the standard
  deviation of each group shows

    SD (Group A) = 3.23
    SD (Group B) = 1.76

  that the samples are spread around the mean value differently.  The standard 
  deviation of Group B is closer to 0 than that of Group A so the samples of the 
  Group B will be closer to the mean value than in Group A as shown below: