if an instrument variable is not a proxy variable, then this variable would become a regressor. what model has proxy variables in it? why is y_1 an omitted variable how to determine if a variable is regressing and omitted what is proxy variable in math how to determine if the proxy variable is an unobservable variable what type of variable is used as a proxy variable? which variables are not directly affected by a proxy variable? which variable is an example of a proxy variable when the regressor for an instrument is not correlated with the unobservable variable which variables are not correlated with each other in the proxy or instrument variable ols which variable would be used as the proxy in an equation in which the variable is not partially correlated with the unobservable variable? what would cause a proxy variable to be omitted what is the proxy variable of an equation can an experiment be an endogeneous proxy variable? can we use proxy variables and instrument variables why do eqs need a proxy variable which variable is an instrument variable what is proxy if the regressor is correlated with the unobservable variable, what does the proxy variable do