The items directly relate to the area of investigation.
A variety from different sources and media (e.g. books, periodicals, popular magazines, newspapers, television documentaries, radio recordings, DVD material, web sites, etc.)
Evidence of quite rigorous selectiveness. This will be demonstrated by the inclusion of 3-5 items excluded from the final catalogue.
Five references which stem from IMDB can be seen as clearly less impressive than references including one from IMDB, one from a fan site, one from a studio or production company site, one from recognised critic, and one from a film festival.