>> it's a little bit of a -- >> dylan sweeney who covers venture capital says investors are willing to pay more because they're worried about missing out on potentially huge returns. >> it's not like there's a formula you can apply or a computation you can do that comes out with the number. i think a lot of what we're seeing right now is a product of just a lot of enthusiasm for technology start-ups. a lot to invest in. a lot of companies doing really interesting things. and investors don't want to miss out so they're willing to pay a higher price. >> and dreessen horowitz say a lot of companies are staying private longer. start-ups are bulking up their revenues which also sends their valuations higher. companies in the public markets play a role in the valuation game as well. professional investors try and model out what a private company could be worth based on the performance of a successful public company with similar financial characteristics. >> another reason for the run-up in valuation, competition among vcs chasing fewer good ideas. >> there are vc funds that have raised enorm