5.1.5.0 SUMMARY In this unit, we started by explaining structural and reduced form of equations which was illustrated by showing that measurement error is not the only probable cause why the fourth Gauss–Markov condition may not be satisfied for which the biasness of simultaneous equations is an example. We then went further to explain the simultaneous equations bias. 5.1.4.0 CONCLUSION In this unit, Simultaneous equations estimation is discussed. The structural and reduced form of equations as it relates to Simultaneous equations model bias is also explained. Clearly, for deeper understanding of the equation models, the students should make a distinction between endogenousand exogenous variables in Simultaneous equations estimation.