domingo, 29 de noviembre de 2015

Maximum Likelihood versus Parsimony and Bayesian inference

Many authors emphasize in parsimony method by resorting to realism, and the simplicity of the assumptions (Goloboff, 2003). While others say that parsimony subject to specific models is the same as Likelihood (Farris, 1983). Below I will discuss some arguments that lower use of parsimony as a method to clarify the evolutionary relationships among organisms. 

First, that offers simplicity parsimony in assumptions does not mean that these are clear and they are the best. Many wonder what really are the assumptions about the evolutionary process that takes parsimony method? Just assume that the offspring having modification with respect to their ancestors? Assumptions parsimony leave many doubts. 

Second, parsimony does not discriminate changes in the branches are more probability or improbable. It not assumed if a branch is more probability to change over another (Sober, 2004). It is, for parsimony no selection for one character over another (Sober, 2002). It is at this point that the Maximum Likelihood method has its advantages. Using evolutionary models allows us from propositions given by the data and calculate the probability given the hypothesis (Goloboff, 2003). In addition to the rate of Likelihood we can measure the strength of the statistical evidence and so choose the topology more Likelihood (Royall, 1999). 

 On the other hand, it is the Bayesian inference method, a probabilistic method like Likelihood uses evolutionary models. This method uses priors basis for calculating the posterior probability of the data given hypothesis. One risk of using priors is that these can become subjective and condition the calculation of posterior probabilities. I personally think that Bayesian inference is a modification of Likelihood, but with more potential for bias given the priors. 


Andrea Lizeth Silva Cala 

Reference

Goloboff, P. A. (2003). Parsimony, likelihood, and simplicity. Cladistics, 19(2), 91-103.

Farris, J. (1983). The logical basis of phylogenetic analysis (pp. 7-36). na.

Sober, E. (2004). The contest between parsimony and likelihood. Systematic biology, 53(4), 644-653.

Sober, E. (2002): “Reconstructing Ancestral Character States – A Likelihood Perspective on Cladistic Parsimony.” The Monist 85: 156-176.

Royall, R. (1999): The Strength of Statistical Evidente. Johns Hopkins University Department of Biostatisks 615 North Wolfe Street Baltimore MD 2120.5 USA