What kind of study When performing an experiment to control for confounding variables such as gender the subjects are separated by that possible confounding variable?

The study described is a stratified randomization or stratified design. In this approach, subjects are divided into groups based on the confounding variable (in this case, gender) before random assignment to experimental conditions. This method helps ensure that the potential influence of the confounding variable is balanced across the treatment groups, thereby enhancing the validity of the experiment's results. By controlling for gender, researchers can more accurately assess the effects of the independent variable on the dependent variable.