be also considered [e.g. @Muno04]. X-ray surveys also suffer some contamination by extragalactic sources, mainly quasars and other active galactic nuclei (AGN) [e.g. @Brandt05]. These can be seen through the Galactic Plane as faint, absorbed X-ray sources.

Careful simulations of contaminating populations can provide estimates for the number of contaminants, their spatial distribution, and some of their apparent X-ray and IR properties. These estimates can inform efforts to assign individual classifications to the detected sources [@Broos11b]. Such simulation studies have been performed for the Orion Nebula Cluster (ONC) and the Cepheus B (Cep B) star-forming regions [@Getman05; @Getman06]. For the deep $Chandra$ observation of the ONC, $150-200$ AGNs, $15-20$ foreground stars, and zero background stars are predicted, constituting $\sim10-15$% of the $>1600$ X-ray detected sources. For the shallow $Chandra$ observation of Cep B, $20-30$ AGNs, $10-15$ foreground stars, and a few background stars are predicted, again $\sim10$% of the $Chandra$ source population.

The number and observed properties of contaminating populations depend on a number of factors: observatory sensitivity, source detection method, observation exposure time, survey field of view, Galactic direction, distance to the star forming region, and absorption through the local molecular cloud. Therefore, it is ill-advised simply to extrapolate 