The number of police officers shot and wounded in the line of duty has spiked from zero to nine this year compared to the same period in 2011, NYPD data shows.

The number of people shot by police has also increased. So far this year, 18 people have been shot by cops compared to 10 over the same period in 2011.

But Nicholas Casale, a former NYPD detective tasked with investigating police-involved shootings, said in the past when there has been a spike in shootings of police officers, there is often a parallel increase in civilians shot by police.

"We saw that during the crack epidemic from around 1982 to 1987. And we also prior to that the end of the 1960s into the early 70s we saw a spike and we attributed it to racial tension," Casale said.

A spokesman for the NYPD said it was too soon to draw any conclusions.

Deputy Commissioner Paul Browne said one incident alone accounted for four of the instances of officers being wounded when an armed Brooklyn man held his pregnant girlfriend and their infant child hostage.

Heather McDonald, a criminal justice expert with the Manhattan Institute, said fluctuations in police interactions with civilians is common.

"I don't think you can say without knowing more and how long this is going to last whether it’s a trend or a coincidence,” said Heather McDonald, a criminal justice expert with the Manhattan Institute.