Nutanix IPO celebration at the Nasdaq market site in New York, September 30, 2016.

Start-up investors showed a jolt of optimism in the third quarter, thanks to some initial public offerings, after a first half with none.

Confidence among venture investors jumped 8 percent in the period, the biggest increase since the first quarter of 2012, according to the Silicon Valley Venture Capitalist Confidence Index. Based on a 5-point scale, confidence rose to 3.88, from 3.6 in the second quarter, the report said.