TABLE 3

Marginal Effects on Probability of Choice of a Chiropractor for a Self-Pay Patient of Median Age, Baseline Oswestry, and Health Opinion Survey Score on the Behavior Subscale

VariableVariable RangeInitial Value of VariableaMarginal Effect on Probability of Choosing a DCb
Baseline Oswestry2–9240−0.0046
Age square324–756916000.000058
HOS score behavior subscale on 9-point scale0–950.02
Trusts MDs (agree = 1)0–10−0.53
Trusts DCs (agree = 1)0–100.21
Against taking prescription drugs (agree = 1)0–110.068
Believes that MDs and DCs are equally skilled in treating LBP (agree = 1)0–10−0.20
Confidence in provider’s ability to successfully treat LBP (has confidence = 1)0–100.18
Payer (reference category: self-pay)
    Oregon Health Plan0–10−0.70
    Insurance0–10−0.52
    Workers’ compensation0–10−0.47
    Auto insurance0–10−0.32
    Other0–10−0.44
Other marital status0–10−0.22
Income > $36 0000–100.064

Note. Oswestry = Revised Oswestry Disability Questionnaire; HOS = Krantz Health Opinion Survey; MDs = medical doctors; DCs = chiropractors; LBP = low back pain.

aFor a patient with these characteristics, the probability of choosing a DC is 0.78.

bThe probability that the event will occur is given by 1 / (1 = e−(βo +β1x1 +.....bκxκ)), where χi are the independent variables and βi are the associated coefficients from Table 2. The marginal effect on probability is an estimate of change in the probability of choosing a DC for a 1-unit increase in the independent variable.