Today was the first day of trading after Nielsen Holdings raised $1.6 billion in the largest private equity-backed IPO since 2006. Shares climbed 11% to $25.58. For its initial public offering, Nielsen sold 71.4 million shares at $23 each; the company had offered the shares at between $20-$22. J.P. Morgan Chase & Co. and Morgan Stanley led the offering. The company back in June filed with the SEC for an initial public offering and said at the time it intended to use the anticipated net proceeds to repay certain existing debt and for general corporate purposes. But the IPO was delayed because market conditions were not ideal.