Effects of measurement error on repeatability of the measured TS ratio.

A. Repeatability (intra-class correlation coefficient) of the TS ratio as measurement error in the two Cq values varies. B. Repeatability of the measured TS ratio (black line, filled circles) and the measured telomere Cq (red circles), as measurement error in the single-copy gene increases. The error σ for telomere is fixed at 0.05. The point where the two lines cross is the point where the advantage of controlling for sample-to-sample variation in the amount of DNA present is offset by the extra measurement error introduced.