Study Design. This was a randomized prospective follow-up study of pai
n facility treatment of chronic pain patients with low back pain, with
return to work and work capacity as the outcome measures. Objectives.
To determine if after pain facility treatment chronic pain patients '
'move''' in and out of work and in their work capacity; to determine t
he patterns of ''movement;'' and to determine the post-pain facility t
reatment follow-up sampling time points that would maximize the number
of chronic pain patients correctly classified according to their fina
l work and work capacity status. Summary of Background Data. Past rese
arch and empiric observation have indicated that chronic pain patients
may ''move'' after pain facility treatment in and out of work and in
their job work capacity. Such ''movement'' can affect the results of o
utcome studies. Methods. Two hundred thirty-six consecutive chronic pa
in patients who fit study selection criteria were followed up at 1, 3,
6, 12, 18, 24, and 30 months after pain facility treatment for determ
ination of work and work capacity status and separated according to th
e pattern of movement. Stepwise discriminant analysis was used to answ
er the study objectives. ''Movement'' in and out of work For these chr
onic pain patients also was compared with the US general population. R
esults. Chronic pain patients demonstrated eight work and four work ca
pacity movement patterns. The 24- and 1-month time paints predicted fi
nal work status correctly far 97.0% and 77.0% of the chronic pain pati
ents, respectively, whereas the most significant predictor for correct
work capacity status was the 24-month point, The annual percentage ch
ange in employment status far these chronic pain patients was more tha
n in the US general population. Conclusions. Because chronic pain pati
ents ''move'' in and out of employment and for work capacity status af
ter pain facility treatment, future outcome studies using these measur
es will have to consider carefully the impact of ''movement'' on their
results.