We study IPOs by focusing on the degree of portfolio diversification of the shareholders taking the company public. We argue that a less diversified shareholder has more to gain from taking the company public and would be more willing to accept a lower price for the sale of its shares, i.e. tolerate higher underpricing. We test these hypotheses by considering all the IPOs that took place in Sweden in the period 1995-2001. We have obtained detailed information on the portfolio composition of all the investors in the companies being taken public, both before and after the IPO, as well as the portfolio composition of investors in similar (in terms of size, book-to-market and industry) companies not taken public. The information is detailed at the stock level, for both private and public companies. We construct several proxies for portfolio diversification of the shareholders and relate them to both the probability of the IPO and the underpricing. We show that companies held by less diversified shareholders are more likely to go public and suffer a higher underpricing. We show that, as predicted, the degree of diversification explains a significant (economically and statistically) part of the probability of going public, and may account for between one third and one half of the reported underpricing. This suggests that the degree of diversification of controlling shareholders should play a prominent role in the discussion of the process of going public.
