Perhaps the most well-known statistical tool is the mean, the arithmetical average of numbers. Add the seven numbers 100, 100, 90, 80, 70, 60 and 50, and you get a sum of 550. Divide 550 by 7, and the result is 78.571428. This is the mean average of the numbers. The result can be rounded off to 78 or 79, for the purpose of the statistics.
Central Tendency, the Median
The median is the middle number in a group. Consider the seven numbers 100, 100, 90, 80, 70, 60 and 50; the middle number is 80. This point divides the numbers in half.
Central Tendency, the Mode
The mode is the most frequent number in a group of data. Of the seven numbers 100, 100, 90, 80, 70, 60 and 50, the most frequent number, and thus the mode, is 100.
Dispersion, the Range
The range illustrates the difference between the highest and lowest number, plus one. Look at the seven numbers 100, 100, 90, 80, 70, 60 and 50. To figure the range, take the highest number, 100, and subtract the lowest number, 50. 100 minus 50 is 50. Now, add 1. In this case, the range of the data is 51.
Dispersion, the Standard Deviation
The standard deviation results from subtracting the mean from all the numbers, and then averaging these differences. Consider the seven numbers 100, 100, 90, 80, 70, 60 and 50. The arithmetic average of adding the numbers and dividing by 7, gives a mean of 78.571428, which can be rounded to 79.
Now, square each number (multiply it by itself) that resulted from subtracting the mean from an original number in the sequence, such as 21 x 21 = 441. That will give you 441, 441, 121, 1, 81, 361 and 841. Added together, the sum is 2287.
Take the sum of the squared numbers, 2287, and divide by 7, the amount
