- ardl fits a linear regression model with lags of the dependent variable and the independent variables as additional regressors. Information criteria are used to find the optimal lag lengths if those are not pre-specified as an option. The estimation output is delivered either in levels form or in equilibrium correction form. The Pesaran, Shin, and Smith (2001) bounds testing procedure for the existence of a levels relationship is implemented as a postestimation command. Corresponding critical values as well as approximate p-values are available for any sample size, number of regressors, and lag combination.