Correlation of ddPCR and qPCR measurements.

<p>(<b>a</b>) Pol copy numbers measured by ddPCR and qPCR were significantly correlated (Pearson R² = 0.64, slope = 0.98±0.08). The correlation weakened at low copy numbers, primarily due to a rapid increase in the variance of the qPCR assay (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055943#pone.0055943.s003" target="_blank">Fig. S3</a> (a)). For copy numbers measured in the bottom tertile (<230 HIV DNA copies/10⁶ cells) by ddPCR, the correlation was not significant (R² = 0.08, P = 0.12). In the central tertile, the correlation was weak but significant (R² = 0.15, P = 0.03). In the top tertile, the correlation was strong (R² = 0.53, P<0.0001). (<b>b</b>) 2-LTR copy numbers measured by both methods were significantly but weakly (R² = 0.14, P = 0.002) correlated.