Her study looks at federal data from 1993 to 2008. During that time, there was a drop in the overall number of mine-related injuries per hours worked, although the number of traumatic injuries has remained fairly flat.
At the same time, the share of the workforce held by union miners declined from just over 21 percent in 1993 to just under 10 percent in 2008.
Simply comparing the number of accidents would produce unhelpful results. As a result, the study reports figures per "man year," a technical measurement of the average time worked in a year.
According to the study, there are .037 traumatic injuries per man year at union mines, compared to .047 traumatic injuries per man year at a nonunion mine. The mortality rate is 0.0003 per man year at union mines and .0006 at nonunion mines.
The total injury rate, which Morantz said is a result of better reporting at union mines, is .126 at union mines versus .115 at nonunion mines.
A spokeswoman for the National Mining Association said there are good safety programs at underground and surface mines; union and nonunion mines; and mines here and abroad.
"I think clearly it's the responsibility of every mine, whether it's union or nonunion, to provide a safe work environment and we're working with all our members who have both kinds of facilities to achieve that objective," the spokeswoman, Carol Raulston, said.
UMWA President Cecil Roberts said the study "quantifies the profound differences" in safety at underground mines depending on their union status.
"As Americans — and especially coal miners — learn about the causes of tragedies like that at the Upper Big Branch mine, one of the things that stands out is that Upper Big Branch, like the other mines where disasters have occurred since 2006, was a nonunion mine," Roberts said. "The simple truth is that union mines are safer mines, and this study proves that."
State House Majority Whip and UMWA member Mike Caputo, D-Marion, said he wants state officials to look at the study.
"My hope is the Board of Coal Mine Health and Safety will look very closely at this study and report back to the Legislature on its findings," Caputo said.
Asked if there were things that nonunion mines could do to achieve the results she found at union mines, Morantz said, "I don't know. That's a question beyond the scope of my study. I hope it's one that future scholars, myself included, will be able to answer someday."
Contact writer Ry Rivard at ry.riv...@dailymail.com or 304-348-1796.