Table 2.

Relative frequency of positive answers for the entry criteria

	Cohort
Criteria	Screening (n=950)	Referral (n=670)	Validation (n=334)
C1: Morning stiffness >30 min	22.0%	30.8%	32.9%
C2: Improvement by movement not by rest	60.4%	72.4%	65.6%
C3: Waking up in the second half of the night because of back pain	38.9%	54.9%	46.4%
C4a: Improvement with NSAIDs within 48 h (in the whole cohort)	44.6%	57.0%	55.4%
C4b: Improvement with NSAIDs within 48 h (if taken)	73.6%	80.9%	76.4%

NSAID, non-steroidal anti-inflammatory drug.