## What is a mean value?

When people talk about an average or middle value, often they are describing the mean. The mean value is the average of all values in a given data set. The mean is a descriptive statistic that measures the center of balance of the data. The higher values are balanced against the lower values.

## How do I calculate a mean value?

In order to find the mean, add all the numbers in the data set, and then divide by the total number of data entries. For example, in the data set {1, 2, 3, 4, 5}; the mean value is (1+2+3+4+5)/5 or 3. In the data set {2,3}, the mean value is 2.5.

## The formula for the mean is ì=Óx/n where:

ì is the Greek letter mu. It represents the mean value of a data set.

Ó is the upper case Greek letter for sigma and is the summation sign. It signifies that all the values following the sign will be added together.

x represents each of the individual values.

n represents the number of values.

## Why is it important to know the mean value?

The mean value is a measure of central tendency. It is a summary statistic that provides us with a description of the entire data set and is especially useful with large data sets where we might not have the time to examine every single value. We can also use the mean to calculate further descriptive statistics, such as the variance and standard deviation. The mean helps us to understand and make sense of our data since it uses all of the data values in the calculation.

## What do I need to know about the mean?

The mean is a very commonly reported summary statistic. It is accurate when the data set is normally distributed. In a normal distribution, the mean, median, and mode are approximately equal to each other. With interval or ratio data, the mean is usually the most useful summary statistic.

However, the mean is affected by extreme values or outliers. This means that in non-normal or skewed distributions (where there are extreme values at one end of the data set), the mean is not a very good summary statistic. The median or mode would provide a more accurate description of the data.

For instance, if ten Microsoft managers with salaries ranging from $50,000 to 70,000 per year were in a room and you took the mean value of all salaries, you might end up with a mean value of approximately $60,000 per year. If Bill Gates walked into the room, the mean value of salaries for people in the room would increase. Here, Bill Gates’ much larger salary has a disproportionate impact on the mean value of all salaries in the room and the mode or median income would describe the entire data set more accurately.

The mean can be calculated for ordinal, interval, or ratio data.