On one level, the University City Science Center in West Philadelphia would appear to be simply a real estate play.

Its string of office buildings stretches along Market Street between 34th and 38th Streets. But as an urban research park, owned by 32 colleges, universities, and research institutions, the science center has sought a higher calling than merely collecting rent.

Started in 1963, the science center began providing "business incubator" services before the concept was even called that. Incubators provide below-market-rate space and shared services to start-up firms that are cash-poor.

So running an incubator really won't make an organization rich, but it can build a legacy as it has for the University City Science Center.

"It's ironic that the business of business incubation has as many hurdles as start-up firms," said president and chief executive officer Stephen S. Tang.

Most start-ups fail in their first two years. So how has the science center done?

Pretty well, a new survey finds. Of the 351 companies that were incubated there since 1968, 155 are still in business; 196 are gone.

That's a 45 percent survival rate. The Economy League of Greater Philadelphia, which prepared the report, said that compares favorably with the 44 percent survival rate calculated by the Bureau of Labor Statistics for all types of businesses between 1998 and 2002.

Ninety-three of the graduating companies are still in the region, while 37 companies are current tenants in West Philadelphia. Those high-tech firms directly employ 15,686 people. Researchers calculated the average wages paid at more than $89,000, compared with the region's average of $54,925.

While I would've picked Malvern or King of Prussia as the most popular destination for post-incubator graduates, the numbers show that 42 kept their 4,980 employees in Philadelphia. Montgomery County attracted 24 firms and 6,935 workers. Chester County gained eight firms and 2,965 jobs.

We'll always wish the impact was even greater. But when you realize that the biggest for-profit employer locally - Lockheed Martin Corp. - has 13,300 employees in the region, what the science center has been able to nurture from its four-block area of the city is impressive.