 Econometric theory uses statistical theory and mathematical statistics to evaluate and develop econometric methods.Econometricians try to find estimators that have desirable statistical properties including unbiasedness, efficiency, and consistency.An estimator is unbiased if its expected value is the true value of the parameter; it is consistent if it converges to the true value as the sample size gets larger, and it is efficient if the estimator has lower standard error than other unbiased estimators for a given sample size.