PEPFAR Quality Control and Method Validation Activity 12 Job Aid 2: Interpreting Comparison Reports

128 Job Aid 2: Interpreting Comparison Reports 1215 When starting your review, begin by asking yourself the following questions: What mean value should my laboratory obtain for this control? What SD or CV do most laboratories achieve with this method? SDI (Standard Deviation Index, a.k.a. z-score) - the calculated value that indicates the number of SD units of each result from the group's mean; describes the bias of a method in units of SD. SDI is expressed as either a positive or negative value, indicating whether your result is above or below the group's mean. For inter-laboratory comparison reports, the SDI is a statistic that indicates the relationship between your mean value and the results reported by your group. SDI = (lab mean - group mean)/group SD CVI (Coefficient of Variation Index, a.k.a CVR) - the comparison or ratio of the laboratory's CV to the group's CV. CVI = lab CV/group CV N - the number of participating laboratories identified in the report SDI CVI 0 Your laboratory's mean value is < 1.0 Indicates for a specific control the the same as the group, no bias imprecision is less than the group's average imprecision + 1.0 Acceptable performance when 1.0 Indicates for a specific control the compared to your group imprecision is the same as the group's average imprecision + 1.0 to 1.9 Problem may exist, laboratory > 1.0 Indicates for a specific control the should investigate problem with imprecision is greater than the bias group's average imprecision + 2.0 or greater Troubleshoot bias problem and > 1.5 Troubleshoot imprecision problem perform corrective action and perform corrective action In addition to the SDI and CVI, inter-laboratory reports often include: 1. Your month's mean, SD, CV, and number of measurements involved. 2. Cumulative or lot-to-date (LTD) laboratory mean, SD, CV, and the number of measurements involved. 3. This month's group mean, SD, CV, and number of measurements involved. 4. Cumulative or lot-to-date (LTD) group mean, SD, CV, and the number of measurements involved. HILS1746 Effective Date: 12/6/2016