Prudential also said it was revising its procedures for appraising its real estate, including the appointment of an independent firm responsible for managing and hiring all appraisal firms.

In 1994, Fendelman created Helaine Fendelman & Associates, a Fine Arts, antiques, and appraisal firm, which she still runs today.

"If there isn't an exclamation point on a description then it's somehow incomplete," said Jonathan J. Miller, the president of Miller Samuel, an appraisal firm.

Corcoran's statistics are based on 20,051 deals - its own and those gathered by a Mitchell, Maxwell & Jackson, an appraisal firm.

He now heads his own appraisal firm.

Mr. Miller, whose appraisal firm has been hired by boards to help prioritize projects, voiced skepticism about the value of a roof deck or any standalone luxury upgrade.

Jonathan J. Miller, the president of Miller Samuel, an appraisal firm, said he also looks at information about similar apartments that are in contract but not yet closed.

He said reputable appraisal firms come up with a fair range of values, but there are also disreputable firms producing unjustifiably low appraisals.

The big increases partly reflected the underpricing of shares by appraisal firms working for directors who planned to buy large blocks of stock themselves at the offering price.

Evelyn Siefert Kennedy owns a textile restoration and appraisal firm in Groton called Sew tique.