Table 1. Sigma value obtained for drugs with quality control level 2 with TEa values 15 and 25.

S. no.	Parameters	October sigma score		November sigma score		December sigma score		January sigma score		February sigma score		Mean sigma score
Abbreviations: AAB, American Association of Bioanalysts; CAP, College of American Pathologists; CFX, Canadian Fixed limits from the College of Physicians and Surgeons of Saskatchewan; CLIA, Clinical Laboratory Improvement Amendments; NYS, New York State Dept. of Health (NYSDOH) Clinical Laboratory Evaluation Program; WLSH, Wisconsin State Laboratory of Hygiene. Sources of TEa: Carbamazepine: TEa = 25 (CLIA, WLSH, AAB, CAP, CFX) TEa = 15 (NYS) Phenytoin: TEa = 25 (CLIA, CAP, CFX, WLSH, AAB) TEa = 15 (NYS). Valproate: TEa = 25 (CLIA, CAP, WLSH, AAB) TEa = 15 (NYS, CFX).
TEa		TEa 15	TEa 25	TEa 15	TEa 25	TEa 15	TEa 25	TEa 15	TEa 25	TEa 15	TEa 25	TEa 15	TEa 25
1	Carbamazepine	1.38	2.75	1.15	2.25	2.05	3.72	2.29	4.70	2.43	4.84	1.86	3.65
2	Phenytoin	-1.82	0.51	1.34	2.63	1.59	5.65	1.26	2.25	1.07	2.06	0.69	2.62
3	Valproate	1.67	5.09	2.31	4.49	4.77	8.26	5.32	10.58	7.03	12.29	4.22	8.14