I came across a post by Matt Bailey called Analytics According to Captain Kirk.  In it, he points out that in Star Trek, the Enterprise has a crew of 430 in its original five-year mission. 80 episodes were produced, during which 59 crewmembers were killed (13.7% of the crew).

* Yellow-shirt crewperson deaths: 6 (10%)
* Blue-Shirt crewperson deaths: 5 (8 %)
* Engineering smock crewperson deaths: 4 (6%)
* Red-Shirt crewperson deaths: 43 (73%)  <<< RED SHIRTS ARE EXPENDABLE!!!

from the Star Trek Inspirational Posters site.