- We considered several scenarios computing the minimum sample size necessary to obtain an estimation of the incidence of resistance among Gram-negative bacteremia episodes with precision equal to 0.05 (preferably) or 0.1, assuming a value between 20% and 60% for the incidence. (Confidence level for the interval estimate always equal to 95%). Scenarios have also been considered for secondary objectives. All calculations were done using the NCSS-PASS 2000 software.