First, the 90K is the Average salary in New York for a cop, that's without benefits
and without overtime :
http://www.indeed.com/salary/q-Police-Officer-l-New-York,-NY.html
This shows the median for all occupations in the USA, as well as the mean :
http://www.bls.gov/oes/current/oes_nat.htm#00-0000
The median wage in the USA is 16.87 / hr.
Without overtime that 16.87/hr comes out to 35,089.
If we compare apples to apples here (no overtime pay) then we are comparing 35,089 to 56,980. Even so, we're still not comparing benefits beyond the 'median' through the country - my guess is pension alone makes the cop job worth another 10k/yr easy, probably more.
But lets stick with what we know.
Cop without overtime : 56,980
Everyone w/o overtime: 35,089
Cops across the country get paid 62% higher than the median for
all other occupations (MANY of which require certifications and/or degrees).
Now if we narrow this down a bit more, what do people who have only a HS diploma or "some college" make?
http://www.infoplease.com/ipa/A0883617.html
In 2010, those with just a HS diploma median was 30,000/yr. Those with a HS diploma + some college median was 33,000.
Note: This is for YEAR ROUND FULL TIME WORKERS ONLY. It wouldn't include people having 2 part time jobs, for example. Obviously, the number would be lower than 30k/33k if it covered everyone.
So what do we have -
For those that hold full time year-round jobs :
Cop with no degree : 56k/yr
Normal person with no degree : 30-33k.
Normal person with an AA degree : 38k
Normal person with Bachelors degree : 47k
Normal person with a Masters Degree : 57k
Normal person with a PHD : 77k
So each step of this way we've given something to the cops that doesn't show here. Overtime, comparison only with those holding full time/ year round jobs, and discounting benefits.
And even with those concessions, a normal person needs a masters degree to make a cops base salary.
And I am pretty sure we're talking about a 'beat cop' here, where the other numbers are medians for many levels of advancement within many fields.