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Weights #505

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jseabold opened this Issue · 5 comments

2 participants

@jseabold
Owner

Make sure weights are correctly handled throughout the models. This includes GLM, RLM, ANOVA, and the discrete choice models. I think it also might make sense to have weights objects. It might also be interesting to see how far we can get with those provided by PySAL, but I haven't spoken with their developers since the summer. Many of their estimators are just duplicating ours. We should make it easy for them to use our code.

@josef-pkt
Owner

I just read this a few days ago

Carroll, Raymond J., and David Ruppert. "Robust estimation in heteroscedastic linear models." The annals of statistics (1982): 429-441.

There are also articles for RLM, M-estimation, with AR(1) and with spatial errors.

So far I don't know what (prior) heteroscedasticity weights would mean in discrete models and the same models in GLM.

@josef-pkt
Owner

to check what matlab has:
robust option in curvefit
http://www.mathworks.com/help/curvefit/least-squares-fitting.html#bq_5kr9-4
and robust regression without a weights options (wfun is our norms M)
http://www.mathworks.com/help/stats/robustfit.html

@josef-pkt
Owner

GLM https://groups.google.com/d/msg/pystatsmodels/QtSH8T47pZg/KYwJCrxD3eYJ
Stata and SAS use weights for loglikeobs w_i * loglike_i
Stata poisson only mentions fweights and pweights (and iweights), but doesn't have aweights.
Stata glm also has aweights but not clear how it's used

more on robust:
Some papers use weighted likelihood to discount influential observations, x outliers
Trimmed MLE uses 0-1 weights for loglike to cut outliers. (same as subset selection in this case).

@josef-pkt
Owner

to the last point: importance weights for Poisson and GLM, question on stackoverflow
http://stackoverflow.com/questions/28951982/using-weightings-in-a-poisson-model-using-statsmodels-module

GEE has weights, #2090

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