Simon Walker writes in The Daily Telegraph

Private equity's critics fairly suggest that there is sometimes nervousness about flotations of companies owned by our industry.

Buyout houses are in the business of transitional ownership. They don't plan to hold a company for decades and then enjoy a bonanza when, say, Kraft comes along and adds another 40% to the share price.

They buy and repair companies that need changing, often combining them with related business that bring real synergies to the entity that emerges. Then they sell the reshaped and improved business, at a profit to their investors - often the same pension funds and insurance companies investing in public markets.

There's no shame in that process. Nor in the fact that buy out houses sometimes get it wrong by asking too much or too little, or mistiming a sale or purchase. But because of its hands-on style and alignment of interests, private equity has historically outperformed listed companies at all stages of the business cycle.

There were no initial private offerings last year and precious few in 2008. A downturn that lasted six quarters and fears of a double-dip recession saw to that.  Perhaps expectations of an IPO bonanza in 2010 grew too far and too fast.

There's now been unsurprising chortling as vaunted private equity flotations have been put on hold.

But it's entirely sensible for big buy out houses to hold back. Their responsibility is to investors, not media commentators, or banks and advisors. There is sensitivity to risk, fears that the Greek crisis could spread across the Eurozone, and a renewed awareness of the possible impact of what Donald Rumsfeld once described as "unknown unknowns".

The banks should have made a fortune bringing BP to market in 1987, but Black Monday torpedoed expectations of an investor windfall. It is understandable - even commendable, that in the most volatile environment in decades, buy out houses are properly cautious with the money they manage on behalf of other people.

So what does history tell us about private equity-backed flotations?

There is hard statistical analysis and the answer is clear:  they outperform other IPOs by nearly 10% and the FTSE All Share Index by 20% one year after their public listing.

Two years ago Cass Business School's Private Equity Centre examined 1735 initial public offerings which raised a total of £70 billion on the London Stock Exchange and AIM markets between 1995 and the end of 2006. Venture capital and private equity accounted for a fifth of these raising 27% of total capital. The private equity backed businesses had spent twice as much on capital expenditure as non-PE  companies, and nearly four times more on research and development.

Far from "buying and flipping", venture and buyout firms invested in businesses for an average of 4 years before flotation, and continued to hold an average of more than 20% of the equity subsequently.  No investors were hit harder when a listing like Debenhams fell than the private equity houses which retained a sizeable stake. But the retail sector had a particularly traumatic recession: just ask the former employees of listed Woolworths, whose directors turned down the private equity bid that might just have saved the company. It is plain wrong to generalise from Debehams to other IPOs.

Buy out houses don't get everything right. But dozens of firms like Crown Paints, TMD Friction,  Poundland, Alliance Boots and New Look are testimony to their ability to renew businesses in the toughest economic crisis.

The boringly prosaic data point that underlies their success was shown in Ernst and Young's analysis of performance arising from Sir David Walker's disclosure guidelines for our previously opaque industry. Productivity in bought-out businesses grew seven times faster than in their competitors. Ultimately that explains why IPOs when they happen bring better returns.

Private equity has changed a lot in the financial crisis. Returns are dependent much less on financial engineering and much more on operational improvement and sheer hard work. However much the moaning minnies mock, buy out houses should exit their ownership as they think appropriate when they believe the time is right.