Lecture 4 Psyc 300A

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Lecture 4Psyc 300A
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Measures of Central Tendency

• Mode The most frequently occurring score
• Median The midpoint in an ordered set of scores.
  The 50th percentile.
• Mean Sum of all scores divided by the number of
  scores.
• Which measure to use?

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Measures of Dispersion

• Range Highest score minus lowest score.
• Standard Deviation Average amount of variability
  in a set of scores. Technically, the square root
  of variance.
• Variance Average squared deviation from the
  mean.

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Formulas to Calculate the SD
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Standard Deviation

• _ _
• X (X X) (X X)2
• 8 2 4
• 8 2 4
• 8 2 4
• 7 1 1
• 6 0 0
• 6 0 0
• 5 -1 1
• 5 -1 1
• 4 -2 4
• 3 -3 9
• sum 0 28
• s Sqrt (28/n-1) 1.76

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Using SPSS

• What is SPSS?
• Setting up a data file
• Running a frequency analysis with descriptive
  statistics