Fig. 2: Fluoride content in 57 samples from 32 households, based on output from the point-of-use biosensor tests and the fluorimeter.
From: The accuracy and usability of point-of-use fluoride biosensors in rural Kenya
a Distribution of fluoride concentrations in 57 water samples, as measured by fluorimeter. The red dashed line indicates the WHO guideline for elevated levels, ≥1.5 ppm. b Representative images of true positive, false positive, true negative, and false-negative test results. Photographs are annotated with fluoride concentrations measured by fluorimeter. c A confusion matrix of test results. “Actual” refers to classification by fluorimeter as being positive (≥1.5 ppm fluoride) or negative (<1.5 ppm fluoride). “Predicted” refers to biosensor test performance. “Negative” means no color change was observed, and “Positive” means a yellow color was visible. True positives and true negatives are shaded in gray, while false positives and false negatives are in white. d Receiver-operating characteristic curve derived from classifications in panel c. Sensitivity is calculated as (true positive)/(true positive + false negative) and specificity is calculated as (true negative)/(true negative + false positive).
