Understanding Z Scores

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Definition of Z Score

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Standard score indicating how many standard deviations an element is from the mean.

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Formula for Z Score

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(X - μ) / σ

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X in Z Score Formula

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The raw score or data point.

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μ in Z Score Formula

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The mean of the population.

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σ in Z Score Formula

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The standard deviation of the population.

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Z Score of 0

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Data point is exactly at the mean.

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Positive Z Score

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Data point is above the mean.

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Negative Z Score

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Data point is below the mean.

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Z Score and Normal Distribution

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Z scores are used to determine the position within a normal distribution.

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Z Score Table

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A table used to find the percentage of values below a certain z score.