At each serial dilution (x axis), parasite densities seen by PCR (open circles) and parasite densities seen by thick blood film examination (filled circles) are both plotted on the y axis. The PCR readings are the result of a single experiment, the thick film readings are the results of two experiments. The solid line (least squares regression line for PCR results against densities known from serial dilution) is given by y = 0.98x + 0.07 (95% CI -0.12 to 0.27). The dotted line (regression line for thick film densities against serial dilution, ignoring the outlier) is given by y = 0.78x - 1.5 (95% CI -0.61 to -2.4) (y = 0.81x - 1.26, 95% CI - 0.07 to -2.5 including the outlier). Densities measured by thick film are therefore approximately 1 log lower than those calculated by serial dilution, whereas PCR readings match the serial dilution more closely.