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The authors have developed and tested scale-up methods, based on a simple social network theory, to estimate the size of hard-to-count subpopulations. The authors asked a nationally representative sample of respondents how many people they knew in a list of 32 subpopulations, including 29 subpopulations of known size and 3 of unknown size. Using these responses, the authors produced an effectively unbiased maximum likelihood estimate of the number of people each respondent knows. These estimates were then used to back-estimate the size of the three populations of unknown size. Maximum likelihood values and 95% confidence intervals are found for seroprevalence, 800,000 +/- 43,000; for homeless, 526,000 +/- 35,000; and for women raped in the last 12 months, 194,000 +/- 21,000. The estimate for seroprevalence agrees strikingly with medical estimates, the homeless estimate is well within the published estimates, and the authors' estimate lies in the middle of the published range for rape victims.

After becoming alarmed about seven unusual and severe complications reported by New York State hospitals after laparoscopic cholecystectomy, the Department of Health of New York State tabulated all reported adverse incidents. After observing unusual injuries to the great vessels of the abdomen and an increase in major bile duct injury during laparoscopic cholecystectomy, the Department of Health prepared a memorandum to New York State hospitals advising closer attention to education, credentialing, proctoring, and outcome after these operations. The frequency of cholecystectomy has increased sharply, by 21%, since the advent of laparoscopic cholecystectomy. The serious injury rate may be approximately 15 times that observed after an open cholecystectomy. Recognizing the theoretic advantages of the procedure, the Department of Health reminded hospital Boards of Trustees of their obligation to establish mechanisms for credentialing and privileging surgeons and surgical teams so that the risks do not exceed those expected of the open procedure and to detect and correct deviations from this standard.