why are nonstationary variables important can you have multiple nonstationary variables in a model what is a simple approach that is not a dummy variable in a forecast? what is the importance of the first difference in the model what is the use of dummies which model uses dummies what's an example of a nonstationary predictor? why do you use dummies instead of models what is the definition of a nonstationary predictor what is the problem of using dummies when using nonstationary variables which is an example of the first difference in a nonstationary variable? what is a nonstationary predictor how do you deal with a critical predictor? when a nonstationary predictor is critically important and can't be captured by first difference what is a critical level predictor nonstationary levels in model when a dummies variable is nonstationary why would we need first differences in a forecast? how to deal with nonstationary variables when a forecaster uses a nonstationary variable what is its importance what is the importance of having one nonstationary predictor