• Antibiotics
• Obesity

American researchers have in the past been hindered in doing population-based child health studies because of the relative lack of comprehensive longitudinal cohort databases, compared to European countries. However this is changing, and a highly controversial paper published in JAMA Pediatrics makes use of a large primary-care based cohort from the area around Philadelphia, involving over 64 500 children from 2001–2013 (Bailey LC and colleagues. 2014. doi:10.1001/jamapediatrics.2014.1539). Linking height and weight data from primary …