what causes the halloween effect 
no one can conclusively identify a reason for this seasonal anomaly while many market watchers believe that the summer vacations of investment professionals impact market liquidity or that investors aversion to risk during the summer months is at least partly responsible for the difference in seasonal returns these notions assume that increased participation means increased gains but market crashes and similar investing disasters are attended by the highest levels in terms of volume and participation therefore the assumption of increased participation may have some correlation with gains but it is not likely to cause the gains proximity to trading resources is not likely to be an explanation either as electronic trading allows investors all around the world to participate as easily from the beach as from the boardroom there is no dearth of theories to support whatever one wants to believe about the halloween strategy for as many different opinions as there are about the halloween effect there is an equal number of theories to support those opinions the halloween strategy is fascinating for the very reason that it is both an empirical anomaly and a mystery 