The Defiant Frog 4000 performed as well, if not better, than traditional dedicated laboratory analytical systems in the performance of BTEX+MTBE analyses. This statement is based on the evaluation of the calibration curve, the low concentration of the MDLs, and the low Z-Scores of the extrenally administered laboratory proficiency studies.
Assigned Value: Value attributed to a particular quantity and accepted, sometimes by convention, as having an uncertainity appropriate for a given purpose. See ISO/IEC 17043 for additional information. In general the assigned value is the value used to assess proficiency and may or may not be the made to value (gravimetric value).
Accept. Window: The range of values that constitute acceptable performance for a laboratory participating in this PT study.
Z: A Z-Score tells how a single data point compare to normal data. A Z-Score says not only whether a point was above or below average, but how unusual the measurement is. Generally, a method result with a Z-Score less than |2| is considered to be in control, a Z-Score between |2| and |3| is considered ‘Questionable’, but still within control and a Z greater then |3| is considered not acceptable and the method is out of control. For WS studies, a z-score greater than |2| is unacceptable. Calculated as Z=(Reported Value – Assigned Value)/Proficiency Std. Dev.