A new study breaks down the risk of male and female service members being sexually assaulted if they are assigned to certain bases and ships, but the data is old and does not explain why some bases pose a higher risk of sexual assault than others, raising questions about how reliable the information in the report really is.

The RAND Corporation study is based on a survey of 170,000 people that it conducted in fiscal 2014. It found that the risks of men and women being sexually assaulted are higher on ships at sea, on bases “with a more prominent combat unit presence,” and at installations with large populations of young and junior ranking service members.

The study also found that the biggest Army and Marine Corps bases have the highest proportion of sexual assaults, including Fort Hood, Texas; Fort Bragg, North Carolina; Fort Lewis, Washington; Fort Campbell, Kentucky; Fort Bliss, Texas; and Camp Lejeune, North Carolina.

However, the study makes clear that it did not determine why the risk of sexual assault is higher at those installations. It cites many possible differences for risk among installations including command climate, the availability and cost of alcohol, crime rates in the surrounding communities, and the transitory presence of sexual predators.

“The one-year rates of sexual assault estimated for each installation should be interpreted descriptively, not as evidence that something about the installation or command is causing or preventing sexual assault,” the study says.

Moreover, the study does not distinguish between on- and off-base sexual assaults.

“They may have occurred in the local community, in off-base housing, during off-base training exercises, or on the installation,” the study says. “For example, when referring to rates of sexual assault for personnel assigned to the USS George Washington, we do not infer that all such assaults occurred while sailors were on that ship. Assaults could also have occurred in the ship’s home port in Norfolk, Virginia; while on liberty at a foreign port; or even while the member was on leave in his or her hometown.”

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The study also acknowledges that the data is four years old, “So it is reasonable to ask whether the distributions of risk we observe in this report have any bearing on risk as it currently exists.”

Still, the study’s authors suspect that the data reflect broad patterns on military bases and ships that are not likely to change quickly.

“We can’t say for sure what is driving these things, but it is certainly possible that there is something that is happening at the installation that is affecting it, but we want to caution people against assuming that’s the case because it could be something going on outside the gates or it could even be factors that we haven’t carefully enough accounted for in our model,” said Andrew R. Morral, one of the study leads.

The RAND study establishes that it is possible to assess the risk of sexual assault on individual bases and ships, which is the type of data that installations commanders have long asked for, Morral told Task & Purpose on Friday.

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The data also reveals sexual assault patterns that should be researched further, he said. For example, it may be possible to identify why sailors on ships are at a higher risk of being sexually assaulted and what the Navy can do about it.

“We think that the greatest value here is in the kind of work that can be done now to start comparing the high and low-risk places and understanding why they are different,” Morral said. “What is it about the low-risk places that seems to be associated with some sort of protective effect for service members?”

The RAND study provides a good starting point for the Defense Department to look into why sexual assault rates are higher at certain bases, said Nate Galbreath, deputy director of the Pentagon’s Sexual Assault Prevention and Response Office.

Right now, the Pentagon does not have enough data to call for changes at the installations identified in the study as having the highest risk for sexual assault because the study does not say why sexual assault rates vary by base, Galbreath told reporters on Friday.

“Unfortunately we don’t know what needs to change, and so telling people, ‘Something needs to change,’ is not going to do anything for folks,” Galbreath said. “What we have to do now is we have to do additional investigation and additional analyses with other methods to actually see what levers to pull to actually bring the occurrence of sexual assault down.”