Table 4.

Data from the epidemiologic literature on back pain at least once in children

	Mikkelsson et al. [ 17 ]	Hakala et al. [ 18 ]	Petersen et al. [ 19 ]	Stanford et al. [ 20 ]	Dunn et al. [ 16 ]	Kjær et al. [ 7 ]
Country	Finland	Finland	Sweden	Canada	USA	Denmark
Design	Cross sectional + follow up	Cross sect. + follow up	Cross sectional	Longitudinal (8 yrs)	Longitudinal (3 m/3 yrs)	Cross sectional + follow up
Study sample	Pupils from 19 primary schools	Population register. All Finns born on adjacent dates in summer	Randomized cluster sample of pupils	Non-institutionalized civilian population	Girls/boys initially 11 yrs randomly selected in GH database	Primary/secondary school. 38 state schools in one municipality
Response rate	83%	77%	97%	?	49%	62%, 57%, 58%
Valid sample size	1756	62677	1121	2488	1333	479, 439, 443
Data collection	Questionnaire	Questionnaire	Questionnaire	Computer ass. Interview + Questionnaire	Telephone survey + Questionnaire	Interview + Questionnaire
Age group	9, 12 (mean: 9.8, 11.8)	12,14,16,18 (mean: 12.6, 14.6, 16.6, 18.6)	6-13	10-18	11-14	9,13,15 (mean: 9.7, 13.1, 15.7)
Definition of back pain	Pain/ache in neck, upper back (UB), low back (LBP)	Back or neck pain the past half a year	Backache last 6 months	Backache past 6 months	Back pain a whole day or more in the past 3 months	Any spinal pain:
Recall period	3 months	6 months	6 months	6 months	3 months	1 month
Prevalence estimates never/seldom	BP (UB, LBP)	BP + NP (12y)	BP (6-13y)	BP (12-13y)	BP (11-14y) 78%	BP (9y, 13y, 15y) 67%
Overall: monthly						33%, 28%, 48%
Frequency	Weekly	Weekly	≥ 1 Weekly:	Weekly	Low/high
Once					10% (low prob.)
Several/frequently/continually	12.7% (Only mentioned in the discussion section)	Girls: 6-16% Boys: 4-10%	Grade 0: 2% Grade 1: 3% Grade 2: 3% Grade 3: 6% Grade 4: 7.5% Grade 5: 14% Grade 6: 17%	17.6%	1,3% (high prob.)