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Equation 1 · Part 2 · One Tree: The Statistics of Common Descent

Symbol P

K=P(D∣MUCA)P(D∣MIO)K = \frac{P(D \mid M_{\text{UCA}})}{P(D \mid M_{\text{IO}})}
PP

What this part means

P is an input to the expression that computes the quantity on the left.

Its job in the formula

P is an input to the expression that computes the quantity on the left.

The passage around this formula

The logic of that adjudication reduces to one ratio. For sequence data compared under a universal-common-ancestry model against an independent-origins model, K=P(D∣MUCA)P(D∣MIO)K = \frac{P(D \mid M_{\text{UCA}})}{P(D \mid M_{\text{IO}})}. and K , the Bayes factor, states exactly how many times more probable the observed data D are under one model than the other - not a correlation coefficient, not a subjective sense of resemblance, but a single number with a precise probabilistic meaning that can in principle come out favouring either model. For the proteins Theobald examined, it was not close. Universal common ancestry came out favoured over the closest competing multiple-ancestry hypothesis by odds reported on the order of ten to the power of two…

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A function assigns an output to each allowed input. The expression f(x) means “apply f to x”.

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