A discussion of the Hawthorne Effect in social experiments and how this effect is estimated in the Health Insurance Study, in which 2000 families are enrolled in different plans that vary the fraction of medical care expenditures the consumer must pay. The Hawthorne Effect states that those involved in an experiment will behave differently simply because they are enrolled in the experiment. It is difficult to measure such an effect, so the experiment is designed to measure effects of certain experimental methods (as opposed to enrollment in the experiment) by splitting the observed sample on the relevant methods, which results in a partial estimate of methods effects. This paper describes those aspects of the experimental design that permit estimating certain methods effects, including (1) the incentive to file claims and the possible stimulus to utilization from frequent questioning; (2) the medical screening examination; (3) the participation incentive payments; and (4) the limited duration of the experiment. 17 pp. Ref.