QC statistics: mean, SD and CV

FREE

Control limits from your control material results.

Note

n = 10 · mean 100 · SD 1.826 · CV 1.83 %. Control limits: ±2 SD 96.35 to 103.65; ±3 SD 94.52 to 105.48.

Reference: Sample standard deviation (n − 1); CV = SD / mean × 100. For learning only. Reference intervals vary by laboratory, method and patient group; results are interpreted by qualified professionals with the clinical picture.

Formula

Mean = Σx / n; SD = √(Σ(x − mean)² / (n − 1)); CV % = SD / mean × 100

Worked example

100, 102, 98, 101, 99 → mean 100, SD 1.58, CV 1.58 %

Limitations

Establish limits from at least 20 results on different days for a new control lot, as most QC guidance recommends.

For learning only. Reference intervals vary by laboratory, method and patient group; results are interpreted by qualified professionals with the clinical picture.