Sample sizes of studies on diagnostic accuracy: literature survey.

OBJECTIVES

To determine sample sizes in studies on diagnostic accuracy and the proportion of studies that report calculations of sample size.

DESIGN

Literature survey.

DATA SOURCES

All issues of eight leading journals published in 2002.

METHODS

Sample sizes, number of subgroup analyses, and how often studies reported calculations of sample size were extracted.

RESULTS

43 of 8999 articles were non-screening studies on diagnostic accuracy. The median sample size was 118 (interquartile range 71-350) and the median prevalence of the target condition was 43% (27-61%). The median number of patients with the target condition--needed to calculate a test's sensitivity--was 49 (28-91). The median number of patients without the target condition--needed to determine a test's specificity--was 76 (27-209). Two of the 43 studies (5%) reported a priori calculations of sample size. Twenty articles (47%) reported results for patient subgroups. The number of subgroups ranged from two to 19 (median four). No studies reported that sample size was calculated on the basis of preplanned analyses of subgroups.

CONCLUSION

Few studies on diagnostic accuracy report considerations of sample size. The number of participants in most studies on diagnostic accuracy is probably too small to analyse variability of measures of accuracy across patient subgroups.