# Using MLE vs. OLS

When is it preferable to use Maximum Likelihood Estimation instead of Ordinary Least Squares? What are the strengths and limitations of each? I am trying to gather practical knowledge on where to use each in common situations.

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As explained here, OLS is just a particular instance of MLE. Here is closely related question, with a derivation of OLS in terms of MLE.

The conditional distribution corresponds to your noise model (for OLS: Gaussian and the same distribution for all inputs). There are other options (t-Student to deal with outliers, or allow the noise distribution to depend on the input)

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(-1) It's not true that the student $t$ can be depended upon to deal with the outliers. See the example here or chapter 2 of this textbook for more explanations. –  user603 Feb 16 '14 at 10:58
The OLS is a distance-minimizing approximation/estimation method, while ML is a "likelihood" maximization method. OLS needs no stochastic assumptions to provide his distance-minimizing solution, while ML starts by assuming a joint probability density/mass function. The fact that in some circumstances the two provide the same solution, in no way does it make the one a particular instance of the other. –  Alecos Papadopoulos Feb 16 '14 at 14:35