<p>Background:</p><p>Recent business paper articles observe that stocks soar when there is a change in ownership. The clothing company JC climbed 26% when it was announced Torsten Jansson had increased his holdings. Daydream, a computer game developer, followed this trend increasing its market value by 17% on the news that TA Capital had increased its hold-ings. In these examples, the market learned of the changes in ownership through a press release created by the acquiring entity. These pieces of news, also known as ownership disclosures, is the target of this thesis.</p><p>Purpose:</p><p>The purpose of this thesis is to investigate whether ownership disclosures result in abnormal stock price changes. Furthermore, the aim is to find out if there are any differ-ences in returns depending on who announced the ownership disclosure. In order to fulfil this purpose, a quantitative approach was used.</p><p>Method:</p><p>A random sample of 160 ownership disclosures is gathered. 77 of these are classified as passive- and 83 as active investors. For each of these pieces of news, 183 days of historical stock price data is retrieved. This data is then parsed through the market model event-study framework.</p><p>Findings:</p><p>Graphically analyzing the whole sample indicates that the market is not efficient in its strong form. The same is true when dividing the sample into passive- and active investors. Statistically, an abnormal return is confirmed for the active investors, but not for the whole sample or the passive investors.</p><p>Conclusion:</p><p>By looking at the price change effects of ownership disclosures, the Stockholm Stock Exchange O-list is determined to be efficient at the semi-strong level. The anomaly caused by active investors leads to the possibility of making a profit of 2.70% between day -1 and day +1 relative to the day of the ownership disclosure being sent out. It should be noted, though, that transaction costs and taxes are not taken into consideration.</p>

Background: Recent business paper articles observe that stocks soar when there is a change in ownership. The clothing company JC climbed 26% when it was announced Torsten Jansson had increased his holdings. Daydream, a computer game developer, followed this trend increasing its market value by 17% on the news that TA Capital had increased its hold-ings. In these examples, the market learned of the changes in ownership through a press release created by the acquiring entity. These pieces of news, also known as ownership disclosures, is the target of this thesis. Purpose: The purpose of this thesis is to investigate whether ownership disclosures result in abnormal stock price changes. Furthermore, the aim is to find out if there are any differ-ences in returns depending on who announced the ownership disclosure. In order to fulfil this purpose, a quantitative approach was used. Method: A random sample of 160 ownership disclosures is gathered. 77 of these are classified as passive- and 83 as active investors. For each of these pieces of news, 183 days of historical stock price data is retrieved. This data is then parsed through the market model event-study framework. Findings: Graphically analyzing the whole sample indicates that the market is not efficient in its strong form. The same is true when dividing the sample into passive- and active investors. Statistically, an abnormal return is confirmed for the active investors, but not for the whole sample or the passive investors. Conclusion: By looking at the price change effects of ownership disclosures, the Stockholm Stock Exchange O-list is determined to be efficient at the semi-strong level. The anomaly caused by active investors leads to the possibility of making a profit of 2.70% between day -1 and day +1 relative to the day of the ownership disclosure being sent out. It should be noted, though, that transaction costs and taxes are not taken into consideration.