Challenges in the Analysis of Longitudinal Pain Data: Practical Lessons from a Randomized Trial of Annular Closure in Lumbar Disc Surgery

Table 2

Unadjusted and integrated VAS pain nonresponders with ACD and controls at each follow-up visit.

Follow-up Interval	Unadjusted			Integrated
	ACD	Control	p-value	ACD	Control	p-value
6 weeks	6.4%	10.7%	0.09	8.3%	15.6%	0.01
3 months	5.3%	6.8%	0.47	7.9%	12.0%	0.15
6 months	4.7%	5.7%	0.69	7.7%	16.6%	0.002
1 year	5.4%	7.7%	0.29	13.0%	25.1%	<0.001
2 years	6.0%	6.7%	0.89	15.7%	27.8%	0.001

Notes:  values represent percentage of patient-reported VAS nonresponders (improvement < 20 points from baseline) recorded at scheduled follow-up visits; values represent percentage of patient-reported VAS nonresponders (improvement < 20 points from baseline) where the baseline VAS pain score was substituted for patient-reported VAS score at the time of symptomatic reherniation and at each subsequent follow-up visit through 2 years using the BOCF approach to represent clinical failure. ACD, annular closure device; BOCF, baseline observation carried forward; VAS, visual analogue scale.