Venn diagram showing: the sample of AGN candidates returned by the RF5 classifier (RF); the sample of AGN candidates from D19; the VST sources in the X-ray sample classified as AGN on the basis of the X/O diagram (X); the VST sources in the main sample classified as AGN on the basis of the MIR diagnostic from Donley et al. (2012); and the VST sources in the main sample classified as AGN on the basis of the criterion defined in Assef et al. (2018). We caution that the area covered by each region is not related to the number of sources in that region. This diagram was rendered via http://bioinformatics.psb.ugent.be/webtools/Venn/.