Shares in private equity group 3i slipped in early trading Thursday as the market expressed dissatisfaction with the company's net asset value performance.The company's diluted net asset value (NAV) per share at the end of September stood at 286p, up from 279.4p at the end of March but well below the 590.3p seen at the end of September 2008.The 2.36% increase in NAV over the first half of the company's financial year compares to a 37% gain in the European Stoxx 600 index over the same period.The company has made a substantial dent in its debt mountain, helped by the proceeds from its £732m right issue.Net debt at the end of September had been reduced to £854m from £1.9bn at the end of March, while gearing had been reduced to 31% from 103%.The balance sheet was further strengthened by the group cashing in on some of its investments. Net realisations exceeded investments in the period by £317m.Gross portfolio return on the opening (end-March) portfolio value was 7.8%, while the total return on shareholders' funds over the period was 3.2%.The company is paying an interim dividend of 1p.'Despite the strong rise in stock markets this year and signs of life in the mergers and acquisitions markets, many major economies remain fragile. We will therefore be taking a measured approach to investment, and continuing to focus on cost discipline,' said Baroness Hogg, chairman of 3I Group.