kalendereffekten

Kalendereffekten is a term used primarily in finance and economics to describe systematic patterns in asset prices, returns or other economic variables that are correlated with the calendar. The name—literally "the calendar effect" in several Scandinavian languages—covers a range of recurring anomalies tied to days of the week, months, holidays or accounting periods.

Common forms include the January effect (abnormally high returns in January), the Monday or weekend effect (lower returns at the start of the week), the turn-of-the-month effect (higher returns around month-ends), and holiday effects (abnormal returns before or after market holidays). Proposed explanations mix behavioral and institutional factors: tax-loss selling and portfolio rebalancing around year-end, reduced liquidity and different trader composition on certain days, window dressing by fund managers, and investor mood or information flow varying with holidays or weekdays.

Empirical evidence is mixed and varies by market, subperiod and asset class. Some calendar effects have weakened or disappeared as markets evolved, trading costs fell, and algorithmic strategies exploited the anomalies. Researchers also caution about data mining and publication bias when assessing statistical significance.

Beyond finance, the concept extends to other disciplines where outcomes show calendar-related patterns, such as retail sales, crime statistics and epidemiology. Understanding kalendereffekten can aid in risk assessment and model specification, but its practical exploitable value is limited by transaction costs, market adaptation and the possibility that observed patterns reflect chance rather than persistent inefficiency.