can a randomised controlled study contain both independent and independent variables? who proposed control for independent and dependent variables how to control for non independent variables in observational study when a non independent variable is controlled in a non-randomized study, how is this justified how is the best way to control for non independent variables in an observational study how is it problematic that a non independent variable is controlled when is it inappropriate to control for independent variables in an observational study why are non independent and independent variables important in an observational study? how is an observational study problematic why do you control for the independent variables in observational studies why is it a problem to control variables can independent covariates be controlled in observational studies? how problematic is it to control for non independent variables in an observational observational study? is it inappropriate to control for independent variable when conducting observational research? why control for non independent covariates why is it problematic for observational studies to control for non-independent variables? why is it problematic to control the independent variables in an observational study? when examining covariance is it problematic why not control for non independent variables in observational study is it problematic to control for non independent covariates in an observational study?