Control variables are variables or elements that are held constant throughout an experiment or research study. They are not of primary interest to the experimenter, but they are controlled because they could influence the outcomes. Control variables are important because they help prevent research biases like omitted variable bias from affecting the results. Any unexpected change in a control variable during an experiment would invalidate the correlation of dependent variables to the independent variable, thus skewing the results and invalidating the working hypothesis. Control variables can be controlled directly by holding them constant throughout a study, or indirectly through methods like randomization or statistical control. Scientists can control variables using several methods, including standardized procedures and processes for all observations, keeping their values constant for all observations in the experiment, and including them in regression analyses and ANCOVAs.