Investigation about a screening step in model selection |
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Authors: | Willi Sauerbrei Norbert Holländer Anika Buchholz |
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Institution: | (1) Stefan-Meier Str. 26, 79104 Freiburg, Germany |
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Abstract: | In many studies a large number of variables is measured and the identification of relevant variables influencing an outcome
is an important task. For variable selection several procedures are available. However, focusing on one model only neglects
that there usually exist other equally appropriate models. Bayesian or frequentist model averaging approaches have been proposed
to improve the development of a predictor. With a larger number of variables (say more than ten variables) the resulting class
of models can be very large. For Bayesian model averaging Occam’s window is a popular approach to reduce the model space.
As this approach may not eliminate any variables, a variable screening step was proposed for a frequentist model averaging
procedure. Based on the results of selected models in bootstrap samples, variables are eliminated before deriving a model
averaging predictor. As a simple alternative screening procedure backward elimination can be used.
Through two examples and by means of simulation we investigate some properties of the screening step. In the simulation study
we consider situations with fifteen and 25 variables, respectively, of which seven have an influence on the outcome. With
the screening step most of the uninfluential variables will be eliminated, but also some variables with a weak effect. Variable
screening leads to more applicable models without eliminating models, which are more strongly supported by the data. Furthermore,
we give recommendations for important parameters of the screening step. |
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Keywords: | Model selection uncertainty Variable screening Bootstrap Simulation |
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