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Psyc_315_-_Winter_2010_-_Class_6

Psyc_315_-_Winter_2010_-_Class_6 - Recap of Last Class The...

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1 Recap of Last Class The Normal Distribution Area Under the Curve Scores Relative to the Mean and Standard Deviation Z Scores Approximation Rule Normal Curve Table • Questions? Chapter 5 Z Scores 3 Standardized Scores Relative Frequency Z Distribution Mean = 0 SD = 1
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4 Steps for Finding Percentages From Scores If you are beginning with a raw score, first transform it to a Z score. Sketch the normal curve, where the Z score falls, and shade in the area for which you are finding the percentage. Make a rough estimate of the shaded area’s percentage based on the 50% - 34% - 14% approximation rule. Find the exact percentage in the normal curve table. 5 Steps for Finding Percentages From Scores If needed, add or subtract 50% from this percentage. • Add: – If the Z score is positive, and you want the total % below this Z score. – If the Z score is negative, and you want the total % above this Z score. 6 Steps for Finding Percentages From Scores If needed, add or subtract 50% from this percentage. • Subtract: – If the Z score is positive, and you want the total % above this Z score. – If the Z score is negative, and you want the total % below this Z score.
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7 Finding Percentages from Scores: Example If a person has an IQ of 125, what percentage of people have higher IQs (mean IQ score is 100 with a standard deviation of 15)? If you are beginning with a raw score, first transform it into a Z score: Z = ( X – M ) / SD = (125 – 100) / 15 = +1.67 Sketch the normal curve, indicate where the Z score falls on it, and shade in the area for which you are finding the percentage.
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