Table 4

Number available for follow up at each time interval

	0 years	5 years	10 years	15 years	20 years
Severe COPD	92	74	54	36	8
Moderate COPD	392	339	290	219	48
Mild COPD	439	398	359	313	62
Respiratory symptoms only	892	812	761	674	99
Restrictive lung disease	511	465	406	328	75
No lung disease	3216	3032	2911	2627	476
Total	5542	5120	4781	4197	768