text: Pain-related clinical variables 
  Pain status was determined using established definitions 
  that account for the duration of pain and activity limita- 
  tions [22, 23] using the following two questions: 1) 
  “How long have you been experiencing your current 
  painful symptoms?” and 2) “Have you experienced ANY 
  pain and activity limitations every day for the past 3 
  months?” Responses to question 1 of “greater than 90 
  days” or responses to question 2 of “Yes” were used to 
  classify patients as having persistent pain at 
  initial 
  evaluation. 
  
  Pain intensity 
  Pain intensity was assessed by the numerical pain rating 
  scale (NPRS) ranging from “0” (no pain) to “10” (worst 