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Why must you square the deviation scores when computing a standard deviation using the definitional formula?

Why is the computational formula easier to use when computing variance and standard deviation?

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kelly
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  1. The sum of the deviations (unsquared) from the mean should always = zero, since the mean serves as a fulcrum (balance point) for the distribution.

    You need to square the sum of the scores rather than the sum of the squared deviations (squaring each scores deviation from the mean).

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    PsyDAG

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