What does Site-Wide False Positive Rate (SWFPR) mean?
Based on the total number of statistical tests performed at a facility (i.e. the number of wells x the number of constituents), the SWFPR reflects the percentage of time you can expect at LEAST one false positive per sampling event. The basic equation for estimating the SWFPR (not including resampling) is the following: SWFPR = 1 (1-alpha)^n Where: alpha = test-wise false positive rate n = number of wells x number of constituents Forthcoming EPA Guidance suggests that the annual SWFPR be no greater than 10% (i.e. 5% per semi-annual event; 2.5% per quarterly event). It goes without saying that the more statistical tests performed at given alpha level at a facility, the higher the SWFPR.
