The number of job openings has increased to levels not seen since the height of the financial crisis, but vacancies are staying unfilled much longer than they used to — an average of 23 business days today compared to a low of 15 in mid-2009, according to a new measure of Labor Department data by the economists Steven J. Davis, Jason Faberman and John Haltiwanger.

Some have attributed the more extended process to a mismatch between the requirements of the four million jobs available and the skills held by many of the 12 million unemployed. That’s probably true in a few high-skilled fields, like nursing or biotech, but for a large majority of positions where candidates are plentiful, the bigger problem seems to be a sort of hiring paralysis.

“There’s a fear that the economy is going to go down again, so the message you get from C.F.O.’s is to be careful about hiring someone,” said John Sullivan, a management professor at San Francisco State University who runs a human resources consulting business. “There’s this great fear of making a mistake, of wasting money in a tight economy.”

As a result, employers are bringing in large numbers of candidates for interview after interview after interview. Data from Glassdoor.com, a site that collects information on hiring at different companies, shows that the average duration of the interview process at major companies like Starbucks, General Mills and Southwest Airlines has roughly doubled since 2010.