Table 5.
Procedures and results of robust Poisson regression analysis of association between treatment success and pyrazinamide use with susceptibilitya
| Factor | Change in coefficient of Z use with susceptibility (%) | Reason for exclusion from multivariable analysis | Adjusted risk ratio (95% CI) |
|---|---|---|---|
| Adverse social factorb | −10.0 | 0.81 (0.64–1.03) | |
| Use of linezolid | 6.7 | <10% change in coefficient | |
| Use of <4 drugs with activity in vitrob | −65.0 | 0.68 (0.51–0.91) | |
| Susceptible to ofloxacin | −31.7 | Multicollinearity | |
| Susceptible to cycloserine | 3.3 | <10% change in coefficient | |
| Z use with susceptibilityb,c | Subgroup A as reference | ||
| Z use with resistance (subgroup B) | 0.723 (0.460–1.135)d | ||
| Z nonuse with susceptibility (subgroup C) | 1.006 (0.792–1.278)e | ||
| Z nonuse with resistance (subgroup D) | 1.062 (0.832–1.355)f |
See footnote a of Table 2 for definitions of abbreviations.
These three factors were included in robust Poisson regression analysis to estimate the adjusted risk ratios of treatment success in the presence of pyrazinamide use with susceptibility in comparison with each of the other alternatives.
In univariate analysis, this factor was evaluated as a binary variable comprising pyrazinamide use with susceptibility as the reference subgroup versus the others. After identifying potential factors that may confound the association between this factor and treatment success, “others” was expanded into three subgroups, namely, pyrazinamide use with resistance, pyrazinamide nonuse with susceptibility, and pyrazinamide nonuse with resistance.
Taking subgroup B (pyrazinamide use with resistance) as the reference group, the adjusted risk ratio becomes 1.38 (95% CI, 0.88 to 2.17), which is the reciprocal of 0.723 (95% CI, 0.460 to 1.135).
Taking subgroup C (pyrazinamide nonuse with susceptibility) as the reference group, the adjusted risk ratio becomes 0.99 (95% CI, 0.78 to 1.26), which is the reciprocal of 1.006 (95% CI, 0.792 to 1.278).
Taking subgroup D (pyrazinamide nonuse with resistance) as the reference group, the adjusted risk ratio becomes 0.94 (95% CI, 0.74 to 1.20), which is the reciprocal of 1.062 (95% CI, 0.832 to 1.355).