Table 4.

Causality of the effect of bDMARDs on spinal radiographic progression in the available literature

Study design	Assumption
	Exchangeability	Positivity	Consistency	Causality
Equal exposure No comparator	–	–	+	Very unlikely
Equal exposure Comparator	+/–	–	–	Unlikely
Variable exposure Comparator	+	+/–	–	Likely

Assumption is very unlikely (–), unlikely (+/–) and likely (+) to be met.