Sign of Predictors in Regression Model

[vishal_prof_gmail_com]

Hi,

In Regression Model , it is possible that a predictor may have positive relation with dependent variable in Bi-variate analysis , however in Model Equation  the predictor may have a negative sign. Why this happens and how is this resolved.

This can happen in Trainin & Validation data as well. That is a predictor may have a Positive sign in the Model equation in Training data set and negative sign in Validation Data-set.

[Norman21]

To me, this indicates a problem somewhere, either in selection of the model, or partitioning of the data into training and validation sets.

Do you have an example that you can post?

[Reeza]

Simpsons Paradox

http://stats.stackexchange.com/questions/1580/regression-coefficients-that-flip-sign-after-including...