2.1 Study criteria
The studies were included if 1) they are published in the English language; 2) they are randomised control trials (RCTs) or a secondary analysis of RCTs; 3) report data from participants aged between 18 and 70 years; 4) only examine people with CLBP (≥ 12 weeks) or have a subgroup for people with CLBP; 5) have at least one therapeutic intervention which is not medication, surgery or an injection intervention, with separate data for this intervention; 6) measure PEs prior to the intervention; 7) examine the association between any type of PEs and the outcomes; and 8) have at least one of the outcomes of pain intensity, physical status and HRQOL.
The studies were excluded if 1) they have participants with other health issues rather than LBP; 2) are a secondary analysis of an RCT study that has already been included in this review; 3) have participants with back pain without specifying its region to the lumber region; and 4) do not state clearly that all participants (or 85% at least) had LBP.