The Thomson Reuters Post-Venture Capital Index (PVCI) is a market-valued index that measures the performance of public stocks of companies that have received financing from a U.S. venture capital firm or buyouts limited partnership prior to going public. The index, which was comprised of 608 companies as of Sept. 30, seeks to track the universe of venture-backed stocks from the point of going public until publicly traded for 10 years.

Companies remain in the index for 10 years from the IPO date or until price data is no longer available, they are acquired or removed from a publicly traded exchange. The index is calculated daily and does not take into account dividends. It began in January 1986 with an initialized index value of 100.

In the wake of the financial sector crisis on Wall Street, which has caused sharp drops in all major U.S. stock indexes, the PVCI plummeted 19% to 511.78 on Sept. 30, down from 631.85 on Aug. 29. That’s the largest monthly percentage plunge since the PVCI declined by 19.41% in September 2001, the month that terrorists attacked the World Trade Center and sent U.S. financial markets into turmoil.

Separately, the PVCI had a market capitalization of $506 billion on Sept. 30, down 18.5% from $620.5 billion a month earlier. A stunning 509 of the stocks tracked by the PVCI declined in September, while just 99 advanced. —Lawrence Aragon