The following plots show the cumulative distribution of sources from the 2MASS Working Database with the various purge flag values in three 10 square degree fields at galactic longitude 90 degrees, and having:

high galactic latitude      (b=90; dashed lines)  [77022 sources]
medium galactic latitude (b=45; solid lines)     [1029574 sources]
low galactic latitude       (b=15; dotted lines)   [1640397 sources]

The fraction of sources is plotted against JHK magnitude for the following purge flags:

Band-filled sources
Glint Flag set
Diffraction Spike Flag set
Stripe Flag set
Confusion Flag set

Since all but the band-filled sources are flagged partly through geometric considerations, the fraction of sources having these purge flags should be inversely correlated with galactic latitude, since the source density increases as one approaches the galactic plane. In other words, fields at a lower galactic latitude have higher numbers of sources that by chance meet the geometric criteria of being flagged as false. As shown in the above plots at positive galactic latitudes, this trend partly holds true: the fields at b=15 have consistently higher fractions of purged sources than the higher galactic latitude fields. However, the same effect is seen when comparing the b=45 and b=90 fields, such that the b=45 field has the lowest fraction of purged sources. One would have expected the b=90 field to have the lowest fraction. More plots are being made at negative latitudes and more intermediate latitudes to investigate this effect further.

For more information on the number of purge flagged sources in the 2nd Incremental Data Release,  see the third table at http://www.ipac.caltech.edu/2mass/releases/second/doc/sec1_6b.html