# Five simple formulas for all 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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## Comments

## why sometimes n and sometimes

why sometimes n and sometimes n-1?

## Use n-1 when you are working

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

## unreal!

unreal!

## Yes yes simple easy

Yes yes simple easy

## The many faces of variance

The many faces of variance