Serum Vitamin A and Inflammatory Markers in Individuals with and without Chronic Obstructive Pulmonary Disease

Table 4

Robust multiple linear regression to identify factors associated with vitamin A concentrations.

Vitamin A (serum)	Dependent variables	Standardized coefficients	value
	Age (years)	0.068	0.620
	Gender (male)	−0.161	0.086
	Smoking status (yes)	0.197	0.042
	IL-6 × CRP × TNF-α (pg/mL)	0.112	0.247
	Presence of COPD (yes)	−0.480	0.001

= 0.26. For robust multiple linear regressions, clinically relevant variables were selected. The included categorical variables were gender (female = 0, male = 1), smoking status (absence = 0, presence = 1), presence of COPD (absence = 0, presence = 1), the interaction of IL-6 × CRP × TNF-α (was considered by multiplying the variables to construct one variable), and age as a continuous variable.