Effect of low retention plastic by concentration. The figure shows the ratio of mean predicted concentrations (C) for low-retention and standard plastic tubes (the ratio is mean(low ret.)/mean(standard)), grouped by nominal concentration (copy number). Note that low-concentration groups include non-amplification events; the ratios partly reflect the reduced incidence of non-amplifications in low-retention tubes. Means were calculated from all observations for concentrations 0.5–1000.