Risk of bias within the individual studies was assessed
using the PEDro scale and results are as follows. One
study scored 9/1114, the second study scored 8/119
, and
the third study scored 9/1115. None of the three studies
met criteria five and six (blinding of all the subjects and of
all therapists administering therapy respectively).
One study15 carried a participant selection bias risk.
All of the participants were recruited through public hospitals,
were unemployed and from low socioeconomic
status. Studies show that CLBP patients from low socioeconomic
status may be harder to treat.16 This may put
the external validity of the study to the general population
into question.
Another study9
may have a participant selection bias.
All the participants were recruited at a public national
health service at their physiotherapy department. These
participants were all referred to this department and had
not sought other choices such as private care or other
health care practitioners that provide spinal manipulation
such as chiropractors, osteopaths, or other practitioners
trained in spinal manipulation. Thus, the external validity
of the results might be questionable