A Poisson specification of the relationship between atmospheric pollution and lost work days is estimated.An important feature of the procedure is control for city-specific effects. A major source of ambiguity in interpreting the results of observational data on pollution versus health status or...

The goal of the paper is to set forth general guidelines that we believe would enhance the usefulness of future social experiments and to suggest ways of correcting for inherent limitations of them. Although the major motivation for an experiment is to overcome the inherent limitations of...