Valuations for Silicon Valley start-ups jumped 64 percent on average in the first quarter. That’s the largest increase since Silicon Valley law firm Fenwick & West started doing surveys in 2002. It is based on financings for 101 Silicon Valley tech start-ups made during the first quarter, where the valuations are compared to start-ups’ previous round.

But let’s wait to see what happens during the second quarter, where we see public stock markets weakening. Venture capitalists follow the lead of public markets, for obvious reasons: If the stock market goes up, it means companies like Google and Yahoo with buoyant stock prices feel wealthy, and are willing to acquire private companies. It also means that start-ups have a better chance of going public. But if the market goes down….

Here is the survey.

The number so-called “up rounds,” where the valuation of a company set during a venture capital investment went up, exceeding the number of “down rounds” for the ninth quarter in a row. And it was the highest margin since the survey began, at 74 percent up vs. 15 percent down, with 11 percent flat.

The Nasdaq was up 6 percent in the first quarter, so you’d expect this sort of thing. However, the Nasdaq is down 7 percent so far in the second quarter, so expect private valuations to taper off.

And there’s conflicting data. According to VentureOne, the average valuation for 177 companies it tracked during the quarter was $20.75 million, down from $21.2 million a year ago. Presumably, this is because VentureOne counts first round investments too, which the Fenwick survey doesn’t include.

Final brightspot: Unpleasant terms such as liquidation preferences are hitting new lows.