Validation of the multiplex PCR–serial dilutions for each set of probes.

<p>A: FAM probes (chromosome 21), B: VIC probes (reference chromosome).</p

Validation of the multiplex PCR.

<p>Validation of the multiplex PCR.</p

Observed vs. theoretical chromosome ratios for mixtures of 0.5 ng/μL DNA with a trisomy 21 DNA content of 0%, 5%, 10%, 25% and 50%.

<p>The solid black line corresponds to local polynomial smoothing of the curve with 95% confidence intervals (dashed lines), and the solid gray line represents the expected relationship.</p

Box-and-whisker/Beeswarm plots of the distribution of chromosome ratios in the two groups (upper plot), and the ROC curve for the chromosome ratio as a predictor of trisomy 21 (lower plot) for samples exceeding the threshold for the number of positive PCRs.

<p>In the upper plot, the box displays the median [25^th-75^th percentiles] for the distribution; the whiskers indicate the data points no further than 1.5 times the interquartile range from the box; crosses represent the group means; data points are plotted as open circles; n = 17 and 187 sample points for the trisomy 21 and normal group respectively. In the lower plot, the AUROC is given with its 95% confidence interval(AUC: Area Under the Curve).</p