For central tendency, we use usually three measures:

Mode - most frequent score

Median - 50% point

Mean - SX/N or the average.

 

• The Mean is the center of normal distributions.
• With skewed distributions, report the mean and median.
• The sum of deviations from the mean equals zero or S (X-Mean) = 0.
• The Mean is unbiased – on the average, sample means aren’t always too high or too low.

• We know can make a frequency distribution and calculate a measure of central tendency.
• Now we need a measure of variability.

For Variability, we use usually two measures:

Range = High score minus Low score

Standard Deviation – A measure of the width of a measurement data distribution