Silver Book Fact
A meta-analysis of pscychological interventions for chronic low back pain found small but statistically significant effects for all interventions for as long as 5 years.
Hoffman B, Papas R, Chatkoff D, Kerns R. Meta-Analysis of Psychological Interventions for Chronic Low Back Pain. Health Psychol. 2007; 26(1): 1-9. http://psycnet.apa.org/journals/hea/26/1/1/