Interpret histogram…
200 participants
                                             [EUR]
about half (71+37=108)÷200 = 54%                (18+28+14=60)÷200 = 30%
of the bills are “small”,                       i.e. nearly a third of the phone bills
i.e. less than 30 EUR                           are greater than 75 EUR
                           There are only a few telephone
                           bills in the middle range.
       Shape of Histograms…
       Symmetry
        A histogram is said to be 
      symmetric if, when we draw a 
      vertical line down the center of the 
      histogram, the two sides are identical 
      in shape and size:
   y                   y                   y
   c                   c                   c
   n                   n                   n
   e                   e                   e
   u                   u                   u
   q                   q                   q
   e                   e                   e
   r                   r                   r
   F                   F                   F
        Variable            Variable            Variable
                                                          2.3
               Bell Shape Histogram – 
          Normal or Gauss distribution
  A special type of symmetric unimodal 
     histogram is one that is bell shaped
      
    Many statistical 
    techniques require that 
    the population be bell 
    shaped.                         y
                                    c
                                    n
                                    e
    Drawing the histogram           u
                                    q
                                    e
                                    r
    helps verify the shape of       F
    the distribution in                Variable
    question.                         Bell Shaped
       Shape of Histograms…
      Skewness (asymmetry)
       A skewed histogram is one with a 
      long tail extending to either the right 
      or the left:
   y                                 y
   c                                 c
   n                                 n
   e                                 e
   u                                 u
   q                                 q
   e                                 e
   r                                 r
   F                                 F
     Variable                          Variable
        Positively Skewed               Negatively Skewed
                                                          2.5
     (left)—Serum albumin values in 248 adults FIG 2 (right)—Normal distribution with the same 
                     mean and standard deviation as the serum albumin values. 
        Altman D G , and Bland J M BMJ 1995;310:298
  ©1995 by British Medical Journal Publishing Group