Publication rate calculated on the basis of the percentage of papers published in a given 2-year period as a percentage of the total in that category over the entire 22-year interval. The slopes of the lines represent the publication rates within the respective categories. Papers catalogued in PubMed demonstrate that observer and performance studies outpaced generic mammographic or mammography standards studies after the mid-1990s, when BI-RADS was increasingly adopted. The search was performed on May 14, 2009. Searches used Medical Subject Heading (MeSH) terms as follows: mammography = “Mammography[MeSH Terms]”; standards = “Mammography/standards[MAJR]”; observer studies = “Mammography[MeSH Terms] AND Observer Variation[MeSH Terms]”; and performance = “Mammography[MeSH Terms] AND Sensitivity and Specificity[MeSH Term].”