The meteoric rise of Uber and other “unicorns”—private, venture-backed companies valued at a billion dollars or more—feels unprecedented. But is it? And does that matter?

Research from Play Bigger, a Silicon Valley consultancy that works with VC-backed start-ups, confirms that they really are growing faster in recent years, at least as measured by market capitalization. It also examines whether raising lots of private capital prior to an IPO is an important determinant of future success and looks at the best time for these companies to go public.

The researchers began by exploring speed. They took the market capitalizations of 1,125 firms started in 2000 or later and divided each by the number of years since founding; the result is the “time to market cap.” A company founded five years ago that’s worth $2 billion, for example, has a greater time to market cap than a company founded 10 years ago that’s worth $3 billion. For firms that have gone public, market cap is the total value of outstanding shares; for private firms, it’s the valuation assigned by VCs during the most recent round of funding. (Private valuations are less precise, but they’re arguably the best approximation of value creation.)

The results were even more dramatic than the researchers expected. Firms founded from 2012 to 2015 had a time to market cap more than twice that of firms founded from 2000 to 2003. In other words, today’s start-ups are growing about twice as fast as those founded a decade ago.

Because the data doesn’t go back to the dot-com era, it’s not clear whether today’s start-ups are getting big more quickly than those of the 1990s. Some of the VCs with whom Play Bigger shared its research suggested that the data merely reflects a bubble. They believe that investors are overpaying for equity in unicorns, thereby inflating their market caps. In November the Financial Times reported that Fidelity Investments had written down its stake in Snapchat—reportedly valued at $15 billion at its last fund-raising, in May—by 25%. Also that month, the mobile payments company Square filed for its IPO at a price range that put the firm’s worth significantly below its private valuation, which was $6 billion in 2014.

Play Bigger founding partner Al Ramadan believes that although a bubble may be part of the explanation for today’s fast growth, fundamental forces are also at work. “Products and services get discovered and adopted at a speed never seen before,” he says. “Word of mouth today—through Facebook, Twitter, Tumblr, Pinterest, and so on—is just so fast, and it’s the most effective means of marketing.” Moreover, the launch of the iPhone, in 2007, not only opened up opportunities for products and services but also created a new way to rapidly distribute software, through the Apple and later the Android app stores.

“Get big fast” has been a start-up mantra since the 1990s. Many VCs try to grow their companies quickly in order to raise as much capital as possible; having a cash hoard, the thinking goes, gives a start-up greater flexibility and more power to fend off potential rivals. But another piece of Play Bigger’s research sounds a cautionary note in this regard.

Specifically, the researchers looked at the 69 U.S. companies in their sample that have raised venture capital since 2000 and subsequently gone public. They wanted to know whether the amount raised prior to IPO predicted growth in market cap after IPO—a proxy for long-term value creation. They found no relationship. “Candidly, we did not expect this result,” says Play Bigger founding partner Christopher Lochhead. “There’s a lot of belief in Silicon Valley that the amount raised really matters.”

If money raised doesn’t predict long-term value creation, what does? The research points to two interesting correlations. The first is the age of the company at IPO. “Companies that go public between the ages of six and 10 years generate 95% of all value created post-IPO,” Ramadan says.

It’s difficult to interpret the finding that company age at IPO predicts value creation, because companies today are not just getting big faster but also staying private longer. And it’s not clear whether the link between firm age and growth in market cap is causal. Are the strongest companies coincidentally all going public at about the same time? Or is there something intrinsic about companies that go public very early or very late that inhibits their ability to create value post-IPO? Play Bigger plans to explore the relationship in future research.