Table 5 Multiple logistic regression analysis to explore possible risk factors, primarily long-term cumulative standing duration, for a pathological reflux (0 = no; 1 = yes), N = 193.

	Model 1				Model 2 (forward-backward-approach)				Model 3				Model 4
	OR	p	lCI	uCI	OR	p	lCI	uCI	OR	p	lCI	uCI	OR	p	lCI	uCI
Intercept	0.539	0.008	0.340	0.844	0.104	0.762	-2.975	0.003	1.388	0.770	0.152	12.517	8.350	0.295	0.163	477.655
Long-term cumulative occupational standing time [in 100 h]	1.001	0.490	0.998	1.004					0.964	0.005	0.938	0.988	0.965	0.010	0.937	0.990
Age (years)					1.031	0.017	1.759	0.079	0.968	0.240	0.917	1.021	0.975	0.389	0.920	1.033
Long-term cumulative occupational standing time [h]* Age (years)									1.001	0.004	1.000	1.001	1.001	0.007	1.000	1.001
Mean period duration [s]													1.000	0.849	0.996	1.005
Gender (ref = women)
Men													0.870	0.687	0.439	1.707
BMI (in kg/m2)													0.956	0.280	0.879	1.036
Education (ref = primary)
Secondary													0.805	0.613	0.347	1.878
Tertiary													1.068	0.916	0.309	3.633
Work ability item 1													0.890	0.319	0.704	1.116
Family history: varicose veins in parents (ref = no)
One parent													1.180	0.624	0.610	2.303
Both													3.038	0.119	0.761	13.073
Smoking habit (ref = non-smoker)
Current					2.541	0.364	2.559	0.010	2.885	0.006	1.376	6.223	2.791	0.014	1.247	6.430
Ex-smoker					2.453	0.382	2.346	0.019	2.690	0.015	1.225	6.038	2.955	0.012	1.283	7.021
AIC	259.5204				252.7402				246.9788				257.8846
AUC	0.47				0.65				0.69				0.71
R²	<0.01				0.08				0.14				0.17

lCI = lower CI; uCI = upper CI; ref = reference category; AIC = Akaike Information Criterion; AUC = Area under the Curve; R² calculated using the pseudo R² by Nagelkerke (1 = best fit); statistically significant results are indicated in bold (p < 0.05).

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