Before revision:  As an application, we analyze the unique dataset of Finnish shareholders throughout 2004-2009 . We find that households play a central role in investor networks, having the most synchronized trading.
After revision:  We use transaction bootstrapping to capture the properties of the actual data generation process and to have a more robust statistical testing procedure. Investor categorization allows for inferring constant size networks and more observations for each node, which is important especially for less liquid securities. We apply this procedure by analyzing a unique data set of Finnish shareholders throughout 2004-2009 . We find that households play a central role in investor networks, having the most synchronized trading.