I found these statistics at the Chronic Pain Association of Canada web site:
The major causes of health-related lost productivity time among American workers, accounting for up to 25% of all sick leave days annually, are:

back pain – an average of 5.8 hours per week for back pain
migraines/headaches – an average of 3.6 hours per week for headache
arthritis – an average of 5.9 hours per week for arthritis

An estimated $90 billion is lost – annually – to American businesses due to chronic pain (sick leave, reduced productivity, medical costs).
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