One of the ways of doing this is to estimate the model in first difference using, for example, the system-GMM estimator. The OLS and within-group estimates are given only as a means of showing that the estimated value of the lagged dependent variable falls between the estimated values obtained using these two methods. This may be viewed as an indication that the bias generated by the presence of endogenous variables and unobservable fixed effects has been corrected for by using the system-GMM method.