Table 4 Estimates of sample sizes (N) per group required to demonstrate (A) significant slope differences between the UC vs., separately, the SIA and SIP group using the pre- vs. post-bronchodilator FEV1 and (B) significant slope differences of 10, 15 and 20 ml/yr for the SIA and the SIP group, separately, vs. a hypothetical comparison group using pre- and post-bronchodilator FEV1, respectively

From: Comparison of the variability of the annual rates of change in FEV₁ determined from serial measurements of the pre- versus post-bronchodilator FEV₁ over 5 years in mild to moderate COPD: Results of the lung health study