CENTRAL TENDENCY
     CENTRAL TENDENCY: descriptive statistics 
    that provide a single score that defines a 
    distribution
      Goal: find the most typical/representative 
     score
                         1    2    3     4    5   
                          6    7
         1   2   3   4   5   6             1   2   3   4   5  6   7 
         7   8   9                          8   9
  MEASURES OF CENTRAL 
  TENDENCY
  Mean
  Median
  Mode
    SAMPLE                 Population 
    MEAN                     Mean
             n                   N
            åx                  åx
       M=i=1                 m=i=1
             n                    N
   Where:
    M = symbol for the mean of sample
    μ = “mu” symbol for mean of population
    ∑ = summation sign
    n or N = number of observations
     CHARACTERISTICS OF THE 
     MEAN
    • The mean is based on all scores in the 
      sample. So….
      Changing the value of any score in the sample will change the 
      mean
      Adding an additional score or taking away a score will change 
      the mean
        (Unless that score is exactly equal to the mean)
     If you add, subtract, multiply or divide a 
      constant value from all scores:
      The mean will change by that value
        Example: add 2 points to every exam grade, mean exam 
        grade will increase by 2 points