central tendency

the central value, the number that scores tend to center around.

Knowing a value or a score does not mean much, unless you have some kind of context. For example, if you were told that an iguana in a zoo laid fifteen eggs, the first question you would ask is: is this a lot? is it a little? What is a typical number of iguana eggs? The key to making sense of the information is knowing what is normal, or typical. This is why central tendency is so important.

However, the mean is not always the best measure. One reason is that the mean is very affected by extreme scores. Consider the following numbers:

1,2,2,2,3,3,4,5,6,7,8,9, 30000.

The average (or "mean") of those scores is 2146.9. Clearly, the average is affected by one very high number, 30000, so it does not accurately reflect the "central tendency" of the other numbers.

To solve this problem, other measures of central tendency can be used such as the median (the middle score, in this case 4), or the mode (the most common score, in this case 2).