Ch 3 Central Tendency

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Ch 3 Central Tendency

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Central Tendency????

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• ???Mean ( )
• ???Median
• ??Mode

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Mean ???

• The most commonly used measure of central
  tendency.
• Formula or
  
• Used for interval, ratio variables (primarily)
  and ordinal variables (sometimes)
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Mean (continued)

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Median ???(Me)

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• The score at the exact center of a distribution
• Used for either ordinal or interval,ratio
  variables
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Mode ??

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• The score that occurs most frequently
• Used for nominal variables
• Used when have a skewed distribution (?????)
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• it can not appropriately represent the center
  of a distribution

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Median vs. Mean

• Median is less sensitive to the extreme scores
• Mean can be affected by the extreme scores
• mean increases when we have more positive extreme
  scores (positive skew)
• mean decreases when we have more negative extreme
  scores (negative skew)
• When and only when a distribution is symmetrical,
  the two means will be the same.

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Measures of Position

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Measures of Position

• Three common measures of position
• Percentile ????
• Deciles ????
• Quartiles ????

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Quartiles

• Quartiles divide the distribution into four
  quarters.
• The first quartile (Q1)25, the second quartile
  (Q2) 50and so forth
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Deciles

• Deciles divide the distribution of scores into
  tenths.
• The first decile 10, the second decile20
  ..and so forth
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Percentile

• Used to determine the location of a score or/ to
  identify the value of a given percentile.
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• 17 18.5 20 25 36 45 57 68 93
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• Q1 Q2 Q3
• D6
• P75

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• 15??????????
• 62 72 39 73 55 90 58 96 83 60 74 76 81 81 72
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• Mean
• Median
• Q1
• Q3
• D60
• P85