Table 3

 Crude and adjusted associations between level of physical activity and number of COPD admissions in COPD subjects (zero-inflated negative binomial regression)

n*Crude IRR(95% CI)p valueAdjusted† IRR(95% CI)p value
IRR, incident rate ratio; CI, confidence interval.
*The number of subjects may be lower in the multivariate models as some values are missing for certain variables (see tables 1 and 2). One subject was excluded from the zero-inflated negative binomial regression model for recording 65 COPD admissions during follow up (outlier value).
†Multivariate model adjusted for sputum and FEV1 in the count component, and for age, ischaemic heart disease, smoking habit, sputum, visits to doctor, and FEV1 in the zero-inflated component of the zero-inflated negative binomial regression.
Physical activity (combined)
    Very low21911
    Low/moderate/high21550.63 (0.46 to 0.86)0.0040.72 (0.53 to 0.97)0.033
Physical activity (categories)
    Very low21911
    Low2940.73 (0.49 to 1.08)0.1130.77 (0.53 to 1.14)0.192
    Moderate10890.63 (0.45 to 0.88)0.0060.68 (0.49 to 0.93)0.018
    High7720.57 (0.40 to 0.82)0.0020.76 (0.53 to 1.08)0.121
p for linear trend0.0020.104