Article type
The proportion of empirical articles peaked in the second period before decreasing (from 47.1% to 32.1%) in the third period. Affirmational non-empirical articles (53.6%) were higher in proportion than affirmational empirical articles (46.0%) in the first period. However, this difference was reversed in the third period, where affirmational empirical articles (29.6%) were higher in proportion than affirmational non-empirical articles (23.4%), (Supplemental digital content 1). Empirical articles (52.9%) were significantly more agenda-setting than non-empirical articles (31.5%) throughout all three periods.