text: commercial insurance coverage on utilization due to the 
  low incidence of these forms of payment in our study 
  sample. Modeling these separately would have created 
  the potential for unreliable and imprecise effect esti- 
  mates. Readers should consider the within-group hetero- 
  geneity caused by this approach and exercise caution 
  when applying these results to individuals who do not 
  have traditional public or private insurance coverage. Fu- 
  ture studies should investigate the performance of the 
  OSPRO tools in predicting outcomes for patients with 
  Worker’s Compensation. 
  
  However, explained variance estimates in our models 
  ranged from 34 to 61%, suggesting further research is 
  necessary to identify additional factors contributing to 
  healthcare utilization following physical therapy. 
  
  The primary limitation of the study is the high number 
  of subjects lost to follow-up. We attempted to account 
  for the bias introduced by loss to follow-up in our 
  models with IPAW, which is a robust strategy for con- 
  ducting analyses with missing data [41, 51]. We observed 
  good concordance between results of complete case and 
  weighted analyses, giving us confidence in our findings. 
  However, important differences in age, race, education, 
  symptom onset, baseline pain intensity, and baseline 
  pain-related psychological distress were noted between 
  those who did and did not complete follow-up. These 
  differences suggest that the group lost to follow-up may 
  represent a unique population to whom these results 
  may not apply. Different factors may predict utilization 
  outcomes for this unique population. As a result, readers 
  should exercise caution when extending these findings 
  to individuals and populations that substantially differ 
  from the analytic sample in this study. Specifically, these 
  predictive models may need to be adjusted for younger 
  individuals of non-white race, with lower education 
  levels, sudden onset of symptoms, and those with higher 
  pain intensity and pain-associated distress. 
  
  A final limitation is the use of patient recall to meas- 
  ure utilization. To mitigate recall bias, we used two 
  follow-up points, at 6 and 12 months. However, under- 
  or over-reporting of utilization is often a concern with 
  studies requiring subject recall [56–58]. Medical record 
  and claims data were not available for these subjects. 
  Readers should consider our inability to independently 
  confirm utilization when interpreting results. 