The Ergonomic Society conducted a study that indicated that many people develop severe back problems during adulthood, and that virtually all such people who received chiropractic treatment showed great improvement. Ttherefore, in order to minimize the proportion of the population that suffers from back pain, the Ergonomic Society recommended that chiropractic treatment be directed toward those adults who suffer from severe back problems. Which of the following is an assumption on which the argument depends? ['Severe back pain and other problems often cause individuals to miss workdays.', 'Chiropractic treatment is more effective in treating severe back problems when utilized over a long period of time, as opposed to sporadically.', 'Individuals who receive chiropractic or other treatment prior to developing severe back problems are not less likely to develop back pain than those who do not.', 'Any person who receives chiropractic treatment for back pain may also benefit from other forms of treatment.']