Reforms of health care financing are controversial because, among other reasons, they might adversely affect public health. Social scientists are expert on many of the mechanisms that could connect these reforms to health. Yet there have been remarkably few attempts by social scientists to contribute to the debate over the health effects of medical care reforms. We suspect that the reasons for this gap include the lack of agreement on a method for such research. We suggest one method and demonstrate its application by testing the hypothesis that the incidence of very low birthweight increased when the financing of health care was changed in four Norwegian communities.