The frequency of patients with IPSS score <8 after three months of treatment with alpha-blockers is about 40%. The sample size required to detect a proportion of 40% with a precision of 0.04 is 550 patients. Based on a literature review of Lacoin et al, the frequency of treated patients with LUTS associated with BPH with an IPSS ≥ 8 is approximately 60%. Thus, 917 patients will be needed to obtain a sample of 550 patients with treatment of alpha-blockers (550/0.6 = 917).