Assumption 1 requires that the dependent variable is a linear combination of the explanatory variables
and the error terms
. Assumption 1 requires the specified model to be linear in parameters, but it does not require the model to be linear in variables. Equation 1 and 2 depict a model which is both, linear in parameter and variables. Note that Equation 1 and 2 show the same model in different notation.
Continue reading CLRM – Assumption 1: Linear Parameter and correct model specification