Was there an error in 1990 census? Because those numbers show an overall population growth of 300,000 over 10 years and Koch was the mayor for that entire period.
Was there an error in the census?
Good grief.
Examining a longer time series (from Appendix table 1 of
http://samoa.istat.it/Eventi/sicurezza/relazioni/Langan_rel.pdf ) ...
the decline of the city started during the tenure of John V. Lindsay and accelerated during the tenure of Abe Beame.
Koch could be said to have stabilized the situation. To be specific, population continued to fall during his first term, and then rebounded to where it was when he took office by the time he left office.
Then there was Dinkins, and the malaise had become perceptible.
Following Dinkins was Guiliani and, very clearly, New York only recovered after Guiliani took office.
The referenced article looks very hard at the FBI crime statistics that are often cited, and asks if the dramatic reduction of crime in New York during Mayor Guiliani's tenure can be verified by independent information.
They look at medical examiner's records of homicides, for example, in addition to the police records on which the FBI crime statistics are based; and, on crimes reported in surveys of the population again in addition to those in the police records.
(It is well known that policie records in many cities understate the amount of crime because of the under-reporting of crime.)
And, yes, the dramatic reduction of crime is verified by independent information.
I could go into the actual record of income and of property values. New York City under Mayor Guiliani did indeed do very well relative to its prior history and relative to the nationwide trends at the time.