Think of Halloween and scares probably are front of mind. Trick or treat. Ghouls and carved pumpkins. In share markets, it appears investor behaviour can also be skewed by scares that accompany dark nights and downbeat emotions associated with the end of summer in the Northern Hemisphere. The phrases “sell in May” (ideally, when prices are high) and “buy on Halloween” (if prices are in a dip) are well known. This “Halloween indicator” will not work every year but research suggests there is some evidence to back it up, on average. It is one of a range of calendar effects that some believe exist in financial markets.