Depending on the age group, 13-38% children reported back pain at least once per survey year, and
5-23% at least twice per survey year. The average weekly prevalence estimate ranged between 1% and 5%. In the
final survey year more girls than boys reported back pain at least twice. The prevalence estimates did not increase
monotonically with age but showed a greater increase in children younger than 9/10, after which they remained
relatively stable up to the age of 12 years.