Chronic and recurrent pain not associated with a disease is very common in childhood and adolescence, but studies of pain prevalence have yielded inconsistent findings. This systematic review examined studies of chronic and recurrent pain prevalence to provide updated aggregated prevalence rates. The review also examined correlates of chronic and recurrent pain such as age, sex, and psychosocial functioning. Studies of pain prevalence rates in children and adolescents published in English or French between 1991 and 2009 were identified using EMBASE, Medline, CINAHL, and PsycINFO databases. Of 185 published papers yielded by the search, 58 met inclusion criteria and were reviewed, and 41 were included in the review. Two independent reviewers screened papers for inclusion, extracted data, and assessed the quality of studies. Prevalence rates ranged substantially, and were as follows: headache: 8-83%; abdominal pain: 4-53%; back pain: 14-24%; musculoskeletal pain: 4-40%; multiple pains: 4-49%; other pains: 5-88%. Pain prevalence rates were generally higher in girls and increased with age for most pain types. Lower socioeconomic status was associated with higher pain prevalence especially for headache. Most studies did not meet quality criteria.

To provide recommendations for the core outcome domains that should be considered by investigators conducting clinical trials of the efficacy and effectiveness of treatments for chronic pain. Development of a core set of outcome domains would facilitate comparison and pooling of data, encourage more complete reporting of outcomes, simplify the preparation and review of research proposals and manuscripts, and allow clinicians to make informed decisions regarding the risks and benefits of treatment. Under the auspices of the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT), 27 specialists from academia, governmental agencies, and the pharmaceutical industry participated in a consensus meeting and identified core outcome domains that should be considered in clinical trials of treatments for chronic pain. There was a consensus that chronic pain clinical trials should assess outcomes representing six core domains: (1) pain, (2) physical functioning, (3) emotional functioning, (4) participant ratings of improvement and satisfaction with treatment, (5) symptoms and adverse events, (6) participant disposition (e.g. adherence to the treatment regimen and reasons for premature withdrawal from the trial). Although consideration should be given to the assessment of each of these domains, there may be exceptions to the general recommendation to include all of these domains in chronic pain trials. When this occurs, the rationale for not including domains should be provided. It is not the intention of these recommendations that assessment of the core domains should be considered a requirement for approval of product applications by regulatory agencies or that a treatment must demonstrate statistically significant effects for all of the relevant core domains to establish evidence of its efficacy.

Prognosis research aims to identify factors associated with the course of health conditions. It is often challenging to judge the overall quality of research evidence in systematic reviews about prognosis due to the nature of the primary studies. Standards aimed at improving the quality of primary studies on the prognosis of health conditions have been created, but these standards are often not adequately followed causing confusion about how to judge the evidence.