Skewness

Skewness is an asymmetrical frequency distribution in which the values are concentrated on one side of the central tendency and trail out on the other side. If the trail is to the right or positive end of the scale, the distribution is said to be positively skewed. If the distribution trails off to the left or negative side of the scale, it is said to be negatively skewed.

Positive Skew


Negative Skew


Sources:

http://www.brendan.com/glossary.html

http://cnx.org/content/m11011/latest/

Measures of Central Tendency

Central Tendency: The center or middle of a distribution. There are many measures of central tendency. The most common are the mean, median, and mode.

http://cnx.org/content/m11011/latest/

Mode

The mode is the most frequently-occurring value (or values).

To calculate the mode:

• Calculate the frequencies for all of the values in the data.

• The mode is the value (or values) with the highest frequency.

Median

The median is the midpoint of a distribution: the same number of observations are above the median as below it

To calculate the median:

• Sort the values into ascending order.

• If you have an odd number of values, the median is the middle value.

• If you have an even number of values, the median is the arithmetic mean (see above) of the two middle values.