Five simple formulas for all parametric statistics

List of the five simple formulas that you need for parametric Statistics.

$$Mean \; formula \quad \bar{X} ={\sum{X} \over {n}}$$
$$Variance \; formula \quad s^2 ={\sum{({X}-{\bar{X})}}^2 \over {n-1}}$$
$$ F \; ratio \; formula \quad F={{MS_{between}} \over {MS_{within}}}$$
$$ Paired \; t-test \; formula \quad {t_{paired}}= {\bar{X}_D \over \sqrt {s^2 \over {n}}}$$
$$t-test \; formula \quad t= {{\bar{X_1}-{\bar{X_2}}} \over \sqrt{{s_1}^2 \over {n_1}}+\sqrt{{s_2}^2 \over {n_2}}}$$

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why sometimes n and sometimes n-1?

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Use n-1 when you are working with samples, that is in analyzing data from experiments.

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unreal!

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Yes yes simple easy

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The many faces of variance

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