Formula to calculate sample size Apply the formula for calculating the sample size of clinical trials comparing the ratio between the two groups: 221112 / 21) qp () qpqp (Z) q. p2 (Z nn In which: (p1, p2 based on the research results of Nakahira J and Akman T) n1: sample size of the control group; n2: sample size of the studying group p1: 76.5% of patients without transurethral resection (TUR) syndrome and hyponatremia with 3% sorbitol irrigating solution.