Table 2. COPD cases and prevalence, by periods and method of estimation.

Method of estimating	2002–2006				2004–2006
prevalence	N	%a	95% CI		N	%a	95% CI
cross-sectional, from HDR	1850	3.16	3.15	3.18	1243	2.11	2.1	2.12
cross-sectional, from all sources	2225	3.83	3.82	3.85	1495	2.56	2.55	2.58
3-yr longitudinal	2544	4.43	4.42	4.45	1985	3.45	3.44	3.46
5-yr longitudinal	---	---			2223	3.87	3.86	3.89

COPD chronic obstructive pulmonary disease; 95% CI 95% confidence intervals.

^aprevalence per 100 40+ year-old residents, standardized by age.