Like so many attempts to compare charter schools to district schools, comparing their suspension rates isn’t straightforward. Here’s what we considered when looking at this data. (Read our full story on those numbers here.)

First, the suspension data we used for district schools comes from the city Department of Education. In 2011-12, the city gave out 69,643 suspensions — 56,385 less-severe “principals’ suspensions,” and 13,258 more-severe “superintendents’ suspensions.” Principals’ suspensions last between one and five days, and students usually serve them in their own school buildings. Superintendents’ suspensions last anywhere from six days to an entire school year, and students are assigned to an alternate learning site.

The city does not release the number of students suspended each year in its reports to the City Council, only the number of suspensions. (Advocates are hoping that will change this year.) But a department spokeswoman told Chalkbeat that 4.2 percent of students were suspended during the 2011-12 year, a number that dropped to 3.4 percent during the 2013-14 year.

We did not use the suspension data collected and presented by the state or federal education department for the city’s district schools. Their figures offer a much lower count of the city’s suspensions, presumably because the city is only required to report out-of-school “superintendents’ suspensions.” But when the city reports suspension numbers to the City Council, it accounts for both in-school and out-of-school suspensions, and we did too.

(Daniel Losen, the director of UCLA’s Center for Civil Rights Remedies who recently completed an analysis of national suspension data collected by the federal education department, said he omitted New York City because of how it appears to under-report suspensions in those datasets.)

We did use the state’s data on charter-school suspensions, because the State Education Department is the only entity that regularly collects it. Its numbers only account for out-of-school suspensions. But since charter schools are free to give out-of-school suspensions for shorter periods than district schools, the data offers a somewhat more complete picture than it would for district schools. Still, the state’s numbers likely underestimate the number of suspensions given by charter schools.

We also used the state’s charter-school enrollment numbers to determine the overall suspension rate for those schools. Getting to that number involved excluding 23 schools for which the state had recorded a 0 percent suspension rate but hadn’t yet opened in 2011-12.

In addition, we verified suspension data with most of the charter schools listed as having especially high rates. We modified the suspension rate of Explore Excel Charter School after a spokeswoman showed that the network had mistakenly reported the total number of suspensions as the number of students it suspended — leading to a 75 percent recorded suspension rate, rather than 18 percent.

It’s also worth noting that all suspension data is self-reported.

At Opportunity Charter School, which had a 37 percent suspension rate in 2011-12, middle school principal Allison Mutzel told Chalkbeat she thinks many schools had similar rates, though not all were as scrupulous at reporting them.

“We actually report the truth,” she said.

View the database we created to analyze suspension rates at city charter schools