Economic transmission planning aims at identifying transmission solutions that reduce system congestion and increase market efficiency. The resulting economic benefits can be quantified by intensive simulations. However, with the rapid increase in the number of transmission proposals for evaluation, the computational requirements may become prohibitive, and therefore it is beneficial to develop an effective and computational efficient screening methodology to screen transmission solutions and identify promising ones for further refinement and full economic evaluation. This paper discusses the guiding principles of an ideal transmission screening method, and proposes a novel LODF-based screening approach. The proposed heuristic yet effective method has been successfully applied in MISO economic transmission planning studies. A case study is provided to demonstrate its effectiveness and advantages.