Table 3.

Firth's logistic regression.

Variable	PE	SE	Wald	Pr $>$ ChiSq	OR	95 % Wald CI
Intercept	$-\mathrm{0.8146}$	0.7255	1.2607	0.2615
Sex
Female	Reference
Male	$-\mathrm{0.1073}$	0.4007	0.0718	0.7888	0.807	0.168	3.881
Previous treatment
Yes	Reference
No	0.0319	0.4341	0.0054	0.9413	1.066	0.194	5.845
Prosthesis type
Revision	Reference
Primary	0.00497	0.4341	0.0001	0.9932	1.010	0.103	9.925
Infection location
Knee	Reference
Hip	0.4090	0.4596	0.7918	0.3736	2.266	0.374	13.731
Cultures
Positive	Reference
Negative	$-\mathrm{0.0601}$	0.5462	0.0121	0.9124	0.887	0.104	7.546
ASA classification
$>\mathrm{3}$	Reference
$<\mathrm{3}$	$-\mathrm{0.7660}$	0.4232	3.3629	0.0667	0.212	0.040	1.113
Soft tissue involvement
Negative	Reference
Positive	$-\mathrm{0.4528}$	0.4887	0.8583	0.3542	0.914	0.175	4.782
Zimmerli infection type
$>\mathrm{24}$ months	Reference
3–24 months	$-\mathrm{0.4528}$	0.4887	0.8583	0.3542	0.404	0.060	2.746
BMI
$>\mathrm{30}$	Reference
$<\mathrm{30}$	$-\mathrm{0.2679}$	0.4548	0.3470	0.5558	0.585	0.098	3.480
Age	0.00717	0.0561	0.0163	0.8983	1.007	0.902	1.124
Time after primary arthroplasty (months)	$-\mathrm{0.00117}$	0.00191	0.3734	0.5412	0.999	0.995	1.003

PE: point estimate, SE: standard error, Wald: Wald test, OR: odds ratio, 95 % Wald CI: 95 % Wald confidence interval, Pr $>$ ChiSq: all predictors equal to zero.