Sample Size Calculation
The equation n= (Zδ2·pq)/d2 was used to figure out the sample size required for each NICU. The lowest rate of off-label drug use with 25.61% in a Chinese NICU was chosen as the assumed rate. The sample size of 1116 in each NICU was expected with a 95% confidence interval. The final sample size was increased to 2400 considering that injection liquid including 0.9% sodium chloride injection, 5% or 10% glucose injection, and sterilized liquid for injection, would be excluded from further study.