Null and alternative hypotheses The primary objective of this study was addressed by a two-sided test at the 0.05 level of significance of the null hypothesis that, in patients with chronic obstructive pulmonary disease (COPD), the bronchodilator efficacy after one month is no greater on tiotropium inhalation capsules (18mcg once daily) than on ATROVENT MDI (2 puffs of 20 mcg q.i.d.), against the alternative hypothesis that the bronchodilator efficacy is greater on tiotropium inhalation capsules (18 mcg once daily).