Associations between chronic comorbidity and exacerbation risk in primary care patients with COPD

Respiratory Research

Table 8 Baseline characteristics of the initial population of all COPD patients, the patients who were lost to follow-up, and the patients with full follow-up

	All COPD patients (n=16,427)	Patients lost to follow-up (n= 1,824)	Patients with full follow-up (study population)^a (n=14,603)
Patient characteristics
Sex, male, n (%)	8,682 (52·9)	933 (51·2)	7,749 (53·1)
Age at study baseline, years; mean (SD; range)	66·9 (11·6; 40–111)	70·1 (12·0; 40–111)	66·5 (11·5; 40–110)^‡
Full dataset available (censored data), n (%)
Full data available	14,603 (88·7)
Deceased	541 (3·0)	541 (29·7)	N/A
Moved	223 (1·3)	223 (12·2)	N/A
Nursing home	36 (0·2)	36 (2·0)	N/A
Unknown	1024 (6·2)	1024 (56·1)	N/A
Comorbidity data
Number of comorbid diseases^b, mean (SD; range)	3·0 (2·3;0–20)	3·4 (2·5; 0–16)	3·0 (2·3;0–20)^‡
Number of comorbid diseases categories^b, n (%)
0	1,951 (11·9)	174 (9·5)	1,777 (12·2)
1 or 2	5,891 (35·9)	586 (32·1)	5,305 (36·6)
3 or 4	4,797 (29·2)	539 (29·6)	4,258 (29·2)
5 and more	3,788 (23·1)	525 (28·8)	3,263 (22·3)^‡
Exacerbations data
Number of exacerbations, mean (SD; range)	0·72 (1·5;0–15)^c	0·46 (1·0;0–11)^c	0·75 (1·5;0–15)

SD standard deviation, N/A not applicable
^* p<0.05, ^† p<0.01, ^‡ p<0.001
^a p-values displayed are calculated for the difference between patients lost to follow-up versus patients with full follow-up. Chi-square tests for categorized variables and independent t-tests for continuous variables. p<0·05 was considered statistically significant
^bPresence of any type of comorbid disease was assessed at study baseline, i.e. 1 January 2012
^cMean number of exacerbations during the study period, 1 January 2012 – 31 December 2013. For the columns ‘all COPD patients’ and ‘Patients lost to follow-up’ these rates cannot be converted into annual rates because of incomplete observation time in the patients who were lost to follow-up
Baseline characteristics of the study population grouped by low (<2/year) versus high (≥2/year) exacerbation rate are reported in Table 1

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