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The MPQ (also called the McGill pain index), is a scale of rating pain developed at McGill University in Canada in 1971. It's a written questionnaire that allows people in pain to give their doctors a good idea of the quality and intensity of pain they're feeling / experiencing. Patients basically choose descriptive words from different categories that best describes their pain.  The MPQ is a well-validated measure of pain with extensive clinical research backing up it's relative accuracy. People can rate their pain in sensory terms (sharp or stabbing, for examples) and choose affective terms (sickening or fearful, for examples), so a doctor or therapist can review 15 total selected descriptors.  Each selected descriptor is rated on a 4-point scale that ranges from none to severe, so the type and intensity of the pain can be better understood by health professionals. The BPI is a questionnaire used to measure pain developed by the Pain Research Group of the WHO Collaborating Center for Symptom Evaluation in Cancer Care. The BPI comes in 2 formats: the short form, which is used for clinical trials; and the long form, which contains additional descriptive items that may be useful to a doctor in a clinical setting. The main purpose of the BPI questionnaire is to assess the severity of a person's pain and the impact it has on their daily functions.  The BPI questionnaire is best for people with pain from chronic diseases, such as cancer, osteoarthritis or low back pain. The BPI can also be used to assess acute pain, such as postoperative pain or pain from accidents and sports injuries. The main areas of assessment for the BPI include: location of pain, severity of pain, impact of pain on daily activities and response of pain levels to medication. The ODI is a numbered index derived from the Oswestry Low Back Pain questionnaire developed in 1980 and used by health care professionals and researchers to quantify disability caused by low back pain. The questionnaire contains 10 topics concerning pain intensity, sexual function, social life, sleep quality and the abilities to lift, sit, walk, stand, travel and care for yourself.  The ODI is a 100-point scale derived from the questionnaire and considered the "gold standard" for measuring disability and estimating quality of life in people with lumbar spinal pain. The severity scores from the questions (ranging from 0-5) are added up and multiplied by two to obtain the index, which ranges from 0-100. Zero is considered no disability, whereas 100 is the maximum disability possible. ODI scores between 0-20 indicate minimal disability, whereas scores between 81-100 indicate either extreme disability (bed-bound) or exaggeration. The questionnaire is more accurate for people with acute (sudden) low back pain than it is for those with chronic (long term) back pain. The TOPS is the longest and most comprehensive survey for patients with chronic pain. The survey is designed to measure quality of life and function for a variety of causes of pain. The TOPS actually contains items from the BPI and ODI questionnaires, as well as questions on coping styles, fear avoidance beliefs, potential substance abuse, satisfaction levels of treatment and demographic variables.  The full TOPS contains 120 items and is about as thorough of a questionnaire that measures pain that you'll come across. TOPS gives quantitative information on pain symptoms, functional limitations, perceived disability, objective disability, treatment satisfaction, fear avoidance, passive coping, solicitous responses, work limitations and life control.  Because of the time it takes to fill out the TOPS, it may not be appropriate for people in severe pain.
Use the McGill Pain Questionnaire (MPQ). Fill out the Brief Pain Inventory (BPI) questionnaire. Use the Oswestry Disability Index (ODI) questionnaire for low back pain. Consider the Treatment Outcomes of Pain Survey (TOPS) instead.