Lastly, and perhaps more critically, theory-based program evaluation relies on monitoring how theory constructs are operationalized over time in order to determine why a set of activities did or did not lead to the desired outcome. The difficulty with monitoring health literacy over time is that, as a social construct, it is developed in response to our expanded cognitive skills as well as the product of social interactions. In essence, health literacy functions as a latent construct - not directly measured, but estimated through proxy measures such as family structure, educational attainment, economic status, health care access, and other contextual factors. Thus, assessing interventions to improve health literacy by measuring proxy covariates over time, while not improbable, can become an evaluator’s nightmare