In addition, we addressed selection bias in the design by constructing separate cohorts in two post-periods that separated the years immediately after the launch of the anti-TNF drugs (2002–2006) where channeling of more severe RA cases to anti-TNF treatment was very strong, from later years (2007–2011) where channeling remained but may have been less severe than that of earlier years [3, 5, 19–21]. Here, TNF is linked to rheumatoid arthritis.