Table:

Comparison of the slopes obtained be each laboratory (y axis) compared to the NMIA testosterone target value (x axis). The slope (a) and intercept (b) are calculated by y=ax +b. These results were obtained using the laboratories own calibrator and are therefore note corrected in any way i.e. prior to recalculation against the CC. All labs (except lab 4) used 1/x weighting for their calibration curve. At the time of this study lab 4 used no weighting - as a result of this study lab 4 moved to 1/x weighting. All samples were run in duplicate and the run was repeated one month later. Results were NOT averaged for the purpose of this comparison. A two tailed paired t-test demonstrated the difference between the means of the slopes were not significantly different i.e. all comparisons had a p>0.05.

Laboratory	RCPAQAP Material Slope	Common Calibrator Material Slope	Unknown Fresh frozen serum Slope
1*	0.986	0.985	1.0399
2*	0.9784	0.9667	0.9989
3**	0.8949	0.9369	0.8915
4**	0.9196	0.9706	0.9406
5*	0.9961	1.0268	0.992
6***	0.9252	1.0834	0.9539
7*	1.0251	1.019	1.0286
8*	1	1	0.9621
Summary of slopes
Minimum slope	0.895	0.937	0.892
Maximum slope	1.025	1.083	1.040
Mean slope	0.966	0.999	0.976
Median slope	0.982	0.993	0.977
SD of slope	0.046	0.045	0.049
Minus 2SD of slope	0.873	0.908	0.878
Plus 2SD of slope	1.058	1.089	1.074
Potential overall difference (95% range) between slopes	19%	18%	20%

^*R² was >0.99 for all materials

^**R² was >0.99 for Common Calibrator & Fresh frozen serum, but < 0.99 for the RCPAQAP material assessment (R²= 0.988 for lab 3) and (R² = 0.9771 for lab 4)

^***R² was >0.99 for the RCPAQAP material, but < 0.99 for the Common Calibrator (R² = 0.9891) and the Fresh frozen serum (R² = 0.9883)

Note: Laboratory 8 was the reference laboratory, i.e. NMIA LC-MS/MS method.