A measure of central tendency (also called measures of center) is a summary that attempts to describe a whole set of data with a single value.

There are three main measures of central tendency: the mode: the most commonly occurring value

the median: the middle value when numbers are in numerical order

the mean: the sum of the values, divided by the total number of items

Measures of Variation:

Variation is a way to show how data is dispersed, or spread out. Several measures of variation are used in statistics.

Range: the difference between the smallest data item in the set and the largest

Quartiles: Quartiles divide your data into quarters - the lowest 25%, the next lowest 25%, the second highest 25% and the highest 25%.

Interquartile Range:

Box and Whisker Plots: a way to organize data into quartiles

Minimum (Lower Extreme): the smallest value in the data set

Maximum (Upper Extreme): the largest value in the data set

Median (Second Quartile): the median of the whole data

Lower Quartile (First Quartile): the median of the lower half of the data

Upper Quartile (Third Quartile): the median of the upper half of the data

Interquartile Range: the difference between the first and third quartile; the length of the box in the box-and-whisker plot; the middle 50%;(Q3 - Q1) = Interquartile Range