Table 3

LINEAR MODELS, variable- oriented hypotheses
Research question Outcome Method of analysis Results from the model data set
All respondents, n = 244 Highly compliant respondents, answering 80% (≥15/18 weeks), n = 161
4A: Association of baseline variables with outcome Weekly recorded pain days, count variable, assuming a binominal distribution Multilevel mixed-effects logistic regression or generalized estimating equation assuming a logit link function (Long previous duration reference category) Subject specific OR = 3.31 (95% CI: 2.1-5.1) Population average OR = 1.96 (95% CI 1.4-2.6) (Note: Interaction duration*week significant) Subject specific OR = 2.67 (95% CI: 1.6-4.5) Population average OR =1.52 (95% CI 1.1- 2.2) (Note: Interaction duration*week significant)
4B: Association of baseline variables with outcome Weekly recorded pain days, count variable, assuming a Poisson distribution Multilevel mixed-effects Poisson regression assuming a log link function (Long previous duration reference category) Subject specific IRR = 1.92 (95% CI: 1.5 – 2.4) (Note: Interaction duration*week significant) Subject specific IRR = 1.82 (95% CI: 1.4 – 2.4) (Note: Interaction duration*week significant)
4 C: Association of baseline variables with outcome Weekly recorded pain days, considered a count variable and assuming a normal distribution Generalized linear regression or mixed linear model assuming an identity link function Average difference in pain days for Long duration – Short duration 1.20 (95% CI: 0.8 – 1.5) (Note: Interaction duration*week significant) Average difference in pain days for Long duration –Short duration 0.95 (95% CI: 0.6-1.4) Note: Interaction duration*week significant)

Axén et al.

Axén et al. BMC Medical Research Methodology 2012 12:105   doi:10.1186/1471-2288-12-105

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