Brief Pain Inventory Severity and Interference Scores: BPI-S and BPI-I are self-reported scales measuring severity of pain and interference on function. Severity scores: 0 (no pain) to 10 (severe pain) on each question assessing worst pain, least pain, and average pain in past 24 hours, and pain right now. Interference scores: 0 (does not interfere) to 10 (completely interferes) on each question assessing interference of pain in past 24 hours for general activity, mood, walking ability, normal work, relations with other people, sleep, and enjoyment of life. Average interference = average of non-missing scores of individual interference items.