There are many clear advantages of using the MPN technique. MPN methodology results in more uniform recovery of a microbial population across different soil types than filter counts. Furthermore, the detection of organisms through process-related attributes often results in the recovery of mixed populations with similar functional roles in soils. For a more detailed study, the mixed populations can be separated into individual colonies. Another advantage of MPN techniques is that, unlike direct quantitative procedures, it measures only live and active organisms. Microscopic techniques sometimes confuse live and dead cells. Also, MPN methodologies provide more realistic estimates of infective propagules of VA mycorrhizae in field soils than does the more conventional method of spore counts. Despite the numerous advantages of using MPN methodology there are a few disadvantages to the method. MPN procedures tend to require more labor and materials than microscopic procedures. Also, MPN estimates often have a lower order of precision than do well-replicated direct counts. Check out this article: http://filebox.vt.edu/users/chagedor/biol_4684/Methods/mpn1.html