A 2005 study was conducted to evaluate the influence of fear avoidance beliefs (FAB), chronicity of low back pain (CHR) and severity of low back pain (SEV) on disability (DIS) in 209 patients from seven different regions in Spain who were treated for low back pain (LBP) in healthcare centers belonging to the Spanish National Health Service. The sample was balanced for acute, subacute, and chronic LBP (i.e. the three categories of the CHR variable). Validated scales and questionnaires were used to assess DIS and FAB during the first visit (day 1) and also 14 days later (day 15). The analyses performed in the study were linear regression analyses using disability measurement (DIS) treated as a continuous outcome variable. However, in the questions to follow, we will treat the disability outcome (DIS) as either a polytomous or an ordinal outcome variable in a logistic regression model. The variables being considered are listed as follows: DIS = disability level at day 15 (0 = none, 1 = mild, 2 = moderate, 3 = severe) FAB = fear avoidance measure at day 1 (0 = low, 1 = high) CHR = chronicity of LBP at day 1 (1 = acute, 2 = subacute, 3 = chronic) SEV = severity of LBP at day 1 (1 = low, 2 = medium, 3 = high) SL = sick leave status at day 1 (0 = not on sick leave, 1 = on sick leave) SEX = male (= 0) or female (= 1) AGE (continuous variable) a. State the logit form of a no-interaction proportional odds logistic model for the relationship of disability outcome DIS to FAB, CHR, SL, SEX, and AGE. Make sure to treat the variables CHR and SEV as nominal (rather than ordinal) variables and to treat AGE as a continuous variable. In stating this model, let "acute" denote the referent category for CHR, and let "low" denote the referent category for SEV. b. Based on the answer in part (a) above, i. What is the formula for the odds for moderate or severe disability (DIS = 2 or 3) to none or mild disability (DIS = 0 or 1) for a subject with high fear avoidance behavior (FAB = 1), chronic low back pain (CHR = 3), and severe low back pain (SEV = 3) who is on sick leave, is female, and is 40 years old? ii. What is the formula for the odds ratio that compares the odds for moderate or severe disability (DIS = 2 or 3) to none or mild disability (DIS = 0 or 1) for a subject with high fear avoidance behavior (FAB = 1), chronic low back pain (CHR = 3), and high severity of low back pain (SEV = 3) to the corresponding odds for a subject with low fear avoidance behavior (FAB = 0), acute low back pain (CHR = 1), and low severity of low back pain (SEV = 1), adjusting for SL, SEX, and AGE? c. Consider the following 4 x 2 table that describes the crude relationship between fear avoidance behavior FAB and disability outcome DIS: FAB DIS 1 0 3 a b 2 c d 1 e f 0 g h