The data were made available by an online broker and cover all transactions since the start of its business in May 1999 up to and including March 2002. The data cover 324,736 transactions in common stocks distributed over 16,831 investors who enter sequentially over time.8 From this sample, investors are then selected if they have been active for at least 12 months and the data on wealth and income are complete. The remaining sample consists of 10,600 investors who made 224,964 common stock transactions distributed over 213,633 investor portfolio months. The average investor is therefore active for approximately 24 months. In addition, with the help of social security numbers, the sample has been matched with the Statistics Sweden database that provides detailed background information on the investors. These data include exact information on the market value of an investor’s total portfolio at each year-end. More importantly, all Swedish financial institutions are legally required to report the market value of all individual’s financial instruments and bank holdings directly to the Swedish Tax Authority. This means that each investor’s total portfolio is observable at yearly intervals, and can be matched to the stocks held with the particular broker under study. Furthermore, information is available on housing wealth (taxable), total liabilities, capital insurance, and income. It is also possible to see if income originates from employment in the financial sector; this may be indicative of better financial decision-making skills.


Trading and Under-Diversification
Anderson (2013)
Review of Finance