What method is used for theory testing by entering all predictor variables into a model simultaneously?

The method used for theory testing that involves entering all predictor variables into a model simultaneously is indeed Forced Entry Regression. This approach allows researchers to analyze the relationships between all independent variables and the dependent variable at the same time, contributing to a comprehensive understanding of how these predictors interact within the context of a specific theoretical framework.

By using this method, researchers can assess the overall model fit and the unique contribution of each predictor while controlling for the others. Forced Entry Regression is particularly valuable when testing hypotheses where all variables are believed to collectively explain variance in the outcome, adhering to a theoretical model that posits relationships among these predictors.

In research, this technique provides a clearer picture of the dynamics at play, as it avoids the biases and potential issues associated with sequentially entering variables, which might obscure the true effects of predictors within the model.