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Section 7 - Using Measures of Central Tendency

Page history last edited by PBworks 16 years, 1 month ago

 

 

Measures of Central Tendency

 

Now do not let this phrase scare you. Measures of central tendency are simply the mean, median, and mode from a set of data.

 

The mean is the average. You find it by adding all of the numbers in a set of data and then dividing that number by the number of terms in the data set.

 

An outlier is a number in a set of data that is either much bigger or smaller than the other numbers.

 

For example: Find the mean.

 

Data set: 2,7,5,23,17,13,21

Add all of the numbers. 2+7+5+23+17+13+21=88.

Count the number of terms or numbers. 7

Divide the sum by the number of numbers. 88/7= 12.6

12.6 is the mean for this set of data.

 

The median is the middle value of a set of data, after it's been arranged in order.  If there are two middle values, find their mean.

 

The mode is the number that occurs the most in a set of data.

 

For example: Find the mode.

 

Data set: 5, 7, 12, 7, 17, 12, 6, 10

There are 2 twelves. Twelve is the mode.

 

Data set: 78, 89, 79, 88, 74, 82, 76

There is only one of each number. There is no mode.

 

Data set: 45,43,50, 54, 32, 45, 47, 47

There are two 45s and two 47s, so there are two modes.

 

The range is the biggest number minus the smallest number.

 

For example: Find the range.

 

Data set: 5, 6, 12, 7, 8, 17, 3, 2

The biggest number is 17. The smallest number is 2. 17-2=15. The range is 15.

 

One way that you can organize your data is in a stem and leaf plot. They look like this:

      key:  1|1 = 11

 

The leaf is the last digit. The stem is the first digits.

 

For example: Make a stem and leaf plot for this set of data.

Data set: 3, 3, 9, 11, 15, 18, 20, 27, 29, 31, 31, 35, 38, 38, 46, 47, 49.

The numbers all are 2 digits or under, so the numbers in the tens place will be the stem. The number in the ones place will be the leaf.  If there is no number in the tens place, just put 0. When you list the leaf numbers, just put a space between them, but nothing else. Keep then in straight columns. When you are done, it should look like this:

          key:  4|6 = 46

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