This article illustrates the commonly overlooked sample selection problem inherent in using rural classification methods that change over time due to population changes. Since fast-growing rural areas grow out of their rural status, using recent rural definitions excludes the most successful places from the analysis. Average economic performance of the areas remaining rural significantly understates true rural performance. We illustrate this problem using one rural classification system, rural-urban continuum codes. Choice of code vintage alters conclusions regarding the relative speed of rural and urban growth and can mislead researchers regarding magnitudes and signs of factors believed to influence growth.