Fig. 4
![Fig. 4](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40345-017-0116-2/MediaObjects/40345_2017_116_Fig4_HTML.gif)
Example of sensitivity and positive predictive value calculation. Calculation of the sensitivity and positive predictive value of Shewhart’s control rules to predict a depressive episode in the next 4 weeks using universal X-bar charts (with mean = 6.2 and SD = 2.5) across a sample of four anonymized patients. QIDS data used in this plot have been imputed using last value carried forward