  A naive Bayes classifier for identifying Class II YSOs has been constructed
and applied to a region of the Northern Galactic Plane containing 8 million
sources with good quality Gaia EDR3 parallaxes. The classifier uses the five
features: Gaia $G$-band variability, WISE mid-infrared excess, UKIDSS and 2MASS
near-infrared excess, IGAPS H$\alpha$ excess and overluminosity with respect to
the main sequence. A list of candidate Class II YSOs is obtained by choosing a
posterior threshold appropriate to the task at hand, balancing the competing
demands of completeness and purity. At a threshold posterior greater than 0.5
our classifier identifies 6504 candidate Class II YSOs. At this threshold we
find a false positive rate around 0.02 per cent and a true positive rate of
approximately 87 per cent for identifying Class II YSOs. The ROC curve rises
rapidly to almost one with an area under the curve around 0.998 or better,
indicating the classifier is efficient at identifying candidate Class II YSOs.
Our map of these candidates shows what are potentially three previously
undiscovered clusters or associations. When comparing our results to published
catalogues from other young star classifiers, we find between one quarter and
three quarters of high probability candidates are unique to each classifier,
telling us no single classifier is finding all young stars.
