  We have used a Galactic sample of OB stars and associations to test the
performance of an automatic grouping algorithm designed to identify
extragalactic OB associations. The algorithm identifies the known Galactic OB
associations correctly when the search radius (78 pc) is defined by the
observed stellar surface density. Galactic OB associations identified with a 78
pc search radius have diameters that are $\sim$3 times larger than OB
associations identified with a 22 pc search radius in M33. Applying the smaller
search radius to the Galactic data matches both the sizes and the number of
member stars between the two galaxies quite well. Thus, we argue that this and
similar algorithms should be used with a constant physical search radius,
rather than one which varies with the stellar surface density. Such an approach
would allow the identification of differences in the giant molecular cloud
populations and star formation efficiency under most circumstances.
