Teacher absenteeism in traditional public schools remains a major problem nationwide, with more than a quarter of teachers using 11 or more sick days in 2013-14, according to a new data analysis.

The report, released Wednesday by the charter school-backed Thomas B. Fordham Institute, combines four data sources to examine chronic teacher absenteeism in traditional public schools and charter schools at the state level.

It shows that about 30 percent of teachers in New York school districts were absent (exclusive of professional development) for more than 10 days in the 2013-14 school year, compared with about 7 percent of teachers in New York charter schools.

The most obvious reason for that disparity is that teachers in traditional public schools belong to unions and have collectively bargained for benefits, including sick time. In New York and elsewhere, districts have tried and mostly failed for decades to stop teachers from using those sick days as personal days, particularly at the end of the workweek.

"Though we cannot prove it, it’s impossible not to sense that the high chronic absenteeism rates for traditional public school teachers are linked to the generous leave policies and myriad job protections that are enshrined in state law and local collective bargaining agreements," the authors wrote. "Because they can’t easily be fired, district teachers can use all their sick and personal days (and get paid for it) without worrying about what their principal or department head will think. But charter school teachers don’t have that luxury."

Driving home that point, the report also shows that teachers in unionized charter schools are much more likely to be chronically absent than those in non-union charter schools, which make up the great majority.

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New York State United Teachers spokesman Carl Korn called the report "an ideological propaganda document," based on out-of-date and incomplete data and conducted by partisans.