Misspecifications of econometric models can lead to biased coefficients and incorrect interpretations of error terms, which in turn can lead to incorrectly estimated models and incorrect inference. There are specific techniques such as instrumental variables, which are used in the economics literature to deal with some individual forms of model misspecification, only addressing one problem at a time. The joint and separate solutions to the problems of unknown functional forms, omitted variables and measurement errors, discussed in this paper, prove that instrumental variables do not exist. Therefore, the specific techniques used in the literature are not feasible. This paper proposes a general method for estimating underlying parameters in the presence of a range of model misspecifications. It is argued that this method can consistently estimate the direct effect of an independent variable on a dependent variable with all of its other determinants held constant even in the presence of an unknown functional form, measurement error and omitted variables.
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