Our thesis researches the Halloween effects in the Swedish stock market from a sector perspective. The notion Halloween effect refers to higher returns during the period November until April than the period May until October. The anomaly has been confirmed by previous researchers in Sweden among other countries. There has not been any definite explanation for this anomaly. The majority of explanations base on the assumption that the anomaly is a market wide and induced by changes in investment behavior. However, previous research has shown that the Halloween effect could be limited to certain sectors which experience significantly higher returns during winter months than the summer months. The sectors that exhibited the high Halloween effect tend to be heavy industry sectors while consumer oriented sectors tend to outperform during summer periods. In our study we research the Swedish sectors to test whether the findings of previous researches are true for other market as well. Our result indicates that the Halloween effect is present in a few sectors and not market wide. The findings thus support previous research that the Halloween effect is sector specific. The sectors that exhibited the highest Halloween effect were sectors in heavy industry.

The Halloween effect refers to higher stock returns during the period November to April compared to May to October. This is a well-known calendar anomaly that has gained a lot of attention due to the fact that the effect is persistent in the market in spite of the fact that investors are aware of the anomaly today. This evokes questions regarding the efficiency in the markets and the Efficient Market Hypothesis in particular. The main focus of this thesis was to investigate whether the Halloween effect still exists in the Swedish stock market and if the power of the effect deviates between different firm sizes. Furthermore, we examined risk differences between the summer -and the winter months, as well as the January effect in order to find out if these could be possible explanations for the Halloween effect and its existence. A trading strategy based on the Halloween effect was also tested in order to see if investors could use this strategy to outperform a buy and hold strategy. The method that was used to investigate the existence of the Halloween effect was Ordinary Least Squares regression models with dummy variables, standard deviation to ascertain risk-differences between the periods and the Sharpe ratio to determine the risk-adjusted returns of the trading strategies. The results showed that the Halloween effect could be found in all of the examined market-cap indices, and therefore the Efficient Market Hypothesis could be questioned. The Halloween effect turned out to be autonomous from the January effect and the risk measured in standard deviation had no significant difference between the summer -and the winter months, hence, both these possible explanations were rejected. The backtesting showed that the Halloween strategy would perform better than the buy and hold strategy in all indices except from the mid-cap index. The results regarding the Sharpe ratio indicated that the Halloween strategy would be a better strategy to use considering risk-adjusted returns as the Sharpe ratio was higher in all indices.

Σκοπός της παρούσας είναι ο έλεγχος της ύπαρξης ημερολογιακών ανωμαλιών στη λειτουργία των διεθνών αγορών, όπως αυτή αποτυπώνεται στην πορεία των χρηματιστηριακών δεικτών κατά την περίοδο 01.01.1988 έως 31.03.2008. Όταν μια ημερολογιακή ανωμαλία γίνεται γνωστή στην αγορά, είναι αναμενόμενο η αντίδραση των επενδυτών στην αναμονή της να βαίνει φθίνουσα με το χρόνο. Για την απόρριψη ή την επιβεβαίωση της υπόθεσης αυτής, στην παρούσα μελέτη, ελέγχεται η ύπαρξη ημερολογιακών ανωμαλιών στις αποδόσεις 15 διεθνών χρηματιστηριακών αγορών τα τελευταία 20 έτη. Κυρίαρχος σκοπός της συγκεκριμένης μελέτης είναι ο έλεγχος της μεταβολής των τάσεων στις προτιμήσεις και τις προσδοκίες των επενδυτών τόσο κατά το πέρασμα των χρόνων όσο και με βάση τη θέση κάθε αγοράς στον παγκόσμιο χάρτη ανάπτυξης. Η εξεταζόμενη περίοδος χωρίζεται σε δύο επιμέρους υποπεριόδους με γνώμονα την διεθνή κρίση που ξεκίνησε στα τέλη του 1999 και επηρέασε καθοριστικά την πορεία της παγκόσμιας οικονομίας. Προσπαθούμε, επομένως, να μελετήσουμε την προσαρμογή των αγορών στις συνθήκες και τα δεδομένα που δημιουργούνται έπειτα από ένα σημαντικό γεγονός. Η μεγάλη βάση του δείγματος - ξεπερνά τα είκοσι έτη, το πλήθος των εξεταζόμενων δεικτών και η προσπάθεια μελέτης διαφορετικών τάσεων με βάση ένα κομβικό σημείο της πορείας της ιστορίας αλλά και με βάση την κατηγοριοποίηση των αγορών ανάλογα με το βαθμό ανάπτυξής τους, διαφοροποιούν την παρούσα μελέτη, και πιστεύουμε ότι αποτελούν ένα ισχυρό κίνητρο για έναν μελετητή ή επενδυτή να αφιερώσει χρόνο στην παρούσα μελέτη. Εξάλλου, τόσο η αξιοσημείωτη διαφοροποίηση των αποτελεσμάτων στις δύο εξεταζόμενες υποπεριόδους, όσο και η χαλαρή τάση που εμφανίζεται σε κάθε κατηγορία αγορών, θεωρούμε ότι δικαιώνουν το εν λόγω εγχείρημα. / When a calendar anomaly becomes acquaintance in the market, the reaction of investors is expected to go declining with the time. For the reject or the confirmation of this affair, in the present study, we check the existence of calendar anomalies in the output of 15 International Stock Exchange markets the last 20 years. The examined period (1988-2008) is separated in two subperiods taking into consideration the international crisis that began in the dues of 1999 in order to be checked the stability of results. The empirical results show important differentiation of results in the two examined subperiods. In any case, the segregation of indicators according to their places in the world market does not appear to attribute substantially conclusions. Specifically in the case of emerging markets, these show that they mark an autonomous movement and to be influenced more by other (internal, mainly) factors.

The financial market anomaly can be characterized as the event when observed stock returns differentiate from those expected by concrete pricing model. Many anomalies have been detected so far, and some of them vanished, while other persisted, after they had been published by academics and researchers. The aim of this thesis is to investigate the potential presence of selected types of anomalies in the financial markets and to provide relevant empirical evidence. The theoretical section will supply the reader with the descriptions of several types of financial market anomalies and the results of past studies documenting the existence of these anomalies, with possible reasons justifying the presence of this phenomenon. The analytical section will focus on the few selected anomalies and test whether they are still present in the selected financial markets.