Outcome variable | Definition | Possible values |
---|---|---|
Pain at present | "Do you at present have pain in the upper part of your back/neck?" Y = 1 if the participants answered yes to the question Y = 0 otherwise | 0, 1 |
A period of pain | "Have you, during the last year, had a period of pain lasting more than 7 days in the upper part of your back/neck?" Y = 1 if the participants answered yes to the question Y = 0 otherwise | 0, 1 |
Number of years with pain | Y = sum of 'a period of pain' over three years (baseline, one-year and two-year follow-ups) | 0, 1, 2, 3 |