


Sherril M. Stone, Ph.D. 

Department of Family Medicine 

OSUCollege of Osteopathic Medicine 





Describes data set 

Affected by outliers 

Outliers skew central tendency and graphs 

Mean 

Median 

Mode 

Standard Deviation 






Population  Greek letter µ 

Sample  letter of the variable with a bar on
top (X bar) 

Formula for Mean 

Xi =
(= 4+7+11+13+13+16+17)/ 7 =
81/7 = 11.5714 @ 11.57
4 

7
Note that the computation of the mean is carried 

11
to four decimals and rounded to two decimal points 

13
at the end of the computation. 

13 

16 

17 





Median 

When scores are in rank order Ð the data score
that is exactly in the middle of all the scores 

If there is an even number of data Ð add middle
two scores and divide by 2 

Mode 

Most frequent score 

May have more than 1 mode 





BellShaped Ð normal distribution 

Skewed 

Positive Ð Mean larger than Median 

Negative Ð Mean smaller than Median 

Others 

Rectangular 

Bimodal 

Jcurves 

