# MEBoost - Novo método para seleção de variáveis

2017 Feb 11
Um dos campos bem pouco explorados em termos acadêmicos é sem sombra de dúvidas a parte de seleção de variáveis. Esse paper trás um pouco de luz sobre esse assunto tão importante e que drena parte do tempo produtivo de Data Scientists.

**MEBoost: Variable Selection in the Presence of Measurement Error -** Benjamin Brown, Timothy Weaver, Julian Wolfson

**Abstract**: We present a novel method for variable selection in regression models when covariates are measured with error. The iterative algorithm we propose, MEBoost, follows a path defined by estimating equations that correct for covariate measurement error. Via simulation, we evaluated our method and compare its performance to the recently-proposed Convex Conditioned Lasso (CoCoLasso) and to the “naive” Lasso which does not correct for measurement error. Increasing the degree of measurement error increased prediction error and decreased the probability of accurate covariate selection, but this loss of accuracy was least pronounced when using MEBoost. We illustrate the use of MEBoost in practice by analyzing data from the Box Lunch Study, a clinical trial in nutrition where several variables are based on self-report and hence measured with error.

**Conclusions**: We examined the variable selection problem in regression when the number of potential covariates is large compared to the sample size and when these potential covariates are measured with measurement error. We proposed MEBoost, a computationally simple descent-based approach which follows a path determined by measurement error-corrected estimating equations. We compared MEBoost, via simulation and in a real data example, with the recently-proposed Convex Conditioned Lasso (CoCoLasso) as well as the naive Lasso which assumes that covariates are measured without error. In almost all simulation scenarios, MEBoost performed best in terms of prediction error and coefficient bias. The CoCoLasso is more conservative with the highest specificity in each case, but sensitivity and prediction are better with MEBoost. In the comparison of selection paths, we saw that MEBoost was more aggressive in identifying variables to be included in the model more quickly than the CoCoLasso. These differences were most apparent when the measurement error had a larger variance and a more complex correlation structure. In addition, MEBoost was 7 times faster than the CoCoLasso. One application of MEBoost took 0.04 seconds versus 0.28 seconds for the CoCoLasso. MEBoost, while a promising approach, has some limitations. One limitation–which is shared with many methods that correct for measurement error–is that we assume that the covariance matrix of the measurement error process is known, an assumption which in many settings may be unrealistic. In some cases, it may be possible to estimate these structures using external data sources, but absent such data one could perform a sensitivity analysis with different measurement error variances and correlation structures, as we demonstrate in the real data application. Another challenging aspect of model selection with error-prone covariates is that, even if the set of candidate models is generated via a technique which accounts for measurement error, the process of selecting a final model (e.g., via cross-validation) still uses covariates that are measured with error. However, we showed in our simulation study that MEBoost performs well in selecting a model which recovers the relationship between the true (error-free) covariates and the outcome, even when using error-prone covariates to select the final model. This finding suggests that the procedure for generating a “path” of candidate models has a greater influence on prediction error and variable selection accuracy than the procedure picking a final model from among those candidates. To conclude, we note that while we only considered linear and Poisson regression in this paper, MEBoost can easily be applied to other regression models by, e.g., using the estimating equations presented by Nakamura (1990) or others which correct for measurement error. In contrast, the approaches of Sørensen et al. (2012) and Datta and Zou (2017) exploit the structure of the linear regression model and it is not obvious how they could be extended to the broader family of generalized linear models. The robustness and simplicity of MEBoost, along with its strong performance against other methods in the linear model case suggests that this novel method is a reliable way to deal with variable selection in the presence of measurement error.