Decomposing mutual fund alpha into security selection and security weighting

I decompose mutual fund alpha into two components: which stocks a mutual fund selects and what weights are placed in those stocks. Although related, each decision has a distinguishable impact on portfolio alpha. I show that deciding how to weight securities is of greater importance than deciding which securities to select. The ability to generate weighting alpha persisting for 12 months while the ability to generate selecting alpha persists for just one. Finally, the performance of mutual funds that both accurately weight and select securities persists for one month and results in significant outperformance.