The U.S. IPO market posted solid numbers in 2012, with 145 companies raising $47 billion in new ­issues, on par with the annual average since 2000, but the figures obscure a wildly uneven year. According to Dealogic, all but one of the year’s top 20 IPO s took place in two periods, one that ran from March 14 to May 17, the other from September 19 to October 25.

The burst of activity in the spring culminated with the $16 billion IPO of Facebook Inc., one of the most widely anticipated new issues ever to debut on a U.S. exchange [Big Deals, July 2012]. Facebook performed poorly in the public markets, as did online gaming company Zynga Inc. [Big Deals, March 2012] and online coupon company GroupOn Inc. [Big Deals, January 2012] in the months after their 2011 IPOs, which helped cool demand not only for technology companies but for those in other industries as well.