An anonymous survey of nearly 2,000 retired officers found that the manipulation of crime reports — downgrading crimes to lesser offenses and discouraging victims from filing complaints to make crime statistics look better — has long been part of the culture of the New York Police Department.

The results showed that pressure on officers to artificially reduce crime rates, while simultaneously increasing summonses and the number of people stopped and often frisked on the street, has intensified in the last decade, the two criminologists who conducted the research said in interviews this week.

“I think our survey clearly debunks the Police Department’s rotten-apple theory,” said Eli B. Silverman, one of the criminologists, referring to arguments that very few officers manipulated crime statistics. “This really demonstrates a rotten barrel.”

Dr. Silverman, professor emeritus at John Jay College of Criminal Justice, and John A. Eterno, a retired New York police captain, provided The New York Times with a nine-page summary of the survey’s preliminary results. After reviewing a copy of the summary, the Police Department impugned the findings on Wednesday. Paul J. Browne, the department’s chief spokesman, criticized the researchers’ methodology and questioned the reliability of the findings.