Bland Altman plot of comparison of Method 1 (Autodelphia) used by centre 1,2,3,4 versus Method 2 (ELISA commercial Biorad) used by centre 5.

<p>Mean difference: −3.854 mU/L (CI −4.291 to −3.417 mU/L) (left) and method 1 (Autodelphia) used by centre 1,2,3,4 versus method 3 (ELISA) used by centre 6; mean difference: −1.470 mU/L (CI −1.692 to −1.249 mU/L) (right).</p

Distribution of TSH values (between 0 and 15 mU/L) over the three different years by the six different scenarios.

***<p>P<0.05 for all Tukey tests comparing differences in TSH levels over the years 2009, 2010, 2011. TSH1: TSH values of centre 5 and 6 converted to Autodelphia method using point estimators for intercept and slope. TSH2: TSH values of centre 5 and 6 converted to Audodelphia method using lower limit of CI for intercept and slope. TSH3: TSH values of centre 5 and 6 converted to Autodelphia method using higher limit of CI for intercept and slope. TSH4: TSH values of centre 5 and 6 converted to Autodelphia method using lower limit of CI for intercept and higher limit of CI for slope. TSH5: TSH values of centre 5 and 6 converted to Autodelphia method using lower limit of CI for slope and higher limit of CI for intercept. TSH6: Only TSH values of 4 centres using Autodelphia method.</p

Regression equations and 95% CI to convert TSH levels of centre 5 and 6 to Autodelphia method.

<p>Centre 5: Liège; Centre 6: Louvain en Woluwé. CI confidence interval.</p

Least square means of difference in TSH among years and seasons, linear mixed model regression.

*<p>transformed values.</p