Measures of Central Tendency

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Measures of Central Tendency
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Line Plots

• Simple graphs that help you see the relationship
  between data items.

x x x x x
x x x x x x x
x x x x x x x x
x x x x x
1 2 3 4 5 6 7 8 9
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Bar Graphs

• Useful when you wish to compare amounts.

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Line Graphs

• Allows you to see how a set of date changes over
  time
• Can only be used when data are continuous

3 2 1
J F M A
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Stem and Leaf Plot

• Displays data items in order
• Almost like a bar graph on its side
• Allows you to see each piece of datum.

Test Scores

• 8 9
• 1 3 5
• 0 1 2 5 7
• 6 7 8 8 8
• 0 0 5

6/8 means 68
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Mean

• Average
• Add up all the scores
• Divide by the number of scores.

5, 7, 3, 2, 2, 4, 0, 1 5 7 3 2 2 4 0
1 24 24/8 3 3 is the mean!
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Median

• Middle score
• Put scores in order from least to greatest or
  greatest to least.
• If there is an even number of scores, take the
  middle two scores, add together and divide by 2.
• If there is an odd number of scores, use the
  middle score.

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Median, cont

• 5, 7, 3, 2, 2, 4, 0, 1 Put these in order
• 0, 1, 2, 2, 3, 4, 5, 7 There are 8 scores, so
  locate the middle two scores (that will be the
  4th and 5th scores)
• 2 and 3 are the middle scores. Add them together
  and divide by 2.
• 2 3 5
• 5/2 2.5
• 2.5 is the median!

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Mode

• Mode is the score that appears the most.
• It might be easier to see this if you put them in
  order first.
• 5, 7, 3, 2, 2, 4, 0, 1
• 0, 1, 2, 2, 3, 4, 5, 7
• Two appears the most, so it is the mode.
• There can be more than one mode. There can be
  no mode (which is NOT the same thing as a mode
  of zero).

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Range and Outliers

• Range is the difference (answer to subtraction)
  between the highest and lowest data points.
• An outlier is a data point that is far from the
  cluster of other data points.