“…A great variation exists in the choice of pain terms: the pain literature is analyzed without any specificity; a large set of pain terms are used; pain synonyms/analogues/related terms (e.g., nociception, analgesia, neuralgia) are employed (30,34,35,47,123); the number of pain terms used may exceed 20 (35, 37, 150) and can be up to 30 (54,79), even though a few studies only use the single word "pain" (80,100,112,140,143). Alternatively, when a specific pain phenomenon is targeted (e.g., fibromyalgia, headache, or low back pain), the choice of painterms is reduced to either one (19,25,108,126,131,133,137,144) or very few (<5) keywords (29,68,69,73,96,155,185).…”