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Objective To compare the rates of hospital admission for management of ovarian cysts in England and Wales and the United States between 1972 and 1974 and 1984 and 1986; and to determine whether these rates are related to rates of early diagnosis of ovarian cancer. Design Analysis of published and unpublished hospital discharge data based on national samples, the Hospital In‐patient Enquiry (HIPE), a 10% hospital discharge sample for England and Wales, and the National Hospital Discharge Survey (NHDs), a 5% sample for the United States. Main outcome measures Age‐specific discharge rates for primary and secondary diagnoses of ovarian cyst or benign ovarian tumour. Results There was an age‐adjusted increase in discharge rates of about 8% in both countries; discharge rates in the United States were approximately double those in England and Wales in both time periods. There was no difference in the rates of early diagnosis of ovarian cancer. Conclusions Ovarian cysts are a common cause of hospital admission in both countries. The higher rates in the United States are not associated with earlier diagnosis of ovarian cancer.

We studied the efficiency of two common sampling strategies used to assemble cohorts to study the long-term problems of preterm infants: infants with birthweights of 500-1499 g, and infants with gestational ages (GA) of < 31 weeks. Birthweight, GA and 2-year outcome data from a population based study of infants < 2001 g, the Central New Jersey Brain Hemorrhage Study (NBH), were used to define the birthweight and GA distributions, at enrollment and at the age of 2 years, of overlapping subsets: infants 500-1499 g (n = 599) and infants < 31 weeks of age (n = 522). Using frequencies from the NBH study, we estimated that 1000 infants of 500-1499 g enrolled at birth would produce 712 infants at the age of 2 years, 498 below 31 weeks and 214 above. Enrolling 1000 infants < 31 weeks would produce a cohort of 697 infants at the age of 2, all of whom were < 31 weeks. Neither sampling strategy maximised the statistical power to investigate the pathophysiological determinants of long-term outcomes associated with short GA. Both methods oversampled older GAs. A stratified sampling technique based on GA, designed to produce equal numbers of subjects at each week of GA, would improve statistical power to study long-term outcomes. As we move from descriptive to analytical studies of preterm infants, we need to devise efficient, GA-based, sampling strategies that maximise statistical power to test pathophysiological hypotheses.

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