To find essential proteins, researchers have used several experimental approaches, such as single gene knockouts (Giaever et al., 2002), RNA interference (Cullen and Arndt, 2005) and conditional knockouts (Roemer et al., 2003), to discover essential proteins. Although many essential proteins have been identified this way, the process is time consuming and expensive. Therefore, with the fast accumulation of available protein–protein interaction (PPI) data, studies on computational methods for predicting essential proteins are attracting increased attention.