New data from the Bureau of Justice Statistics suggest that the amount of incarcerated military veterans in the United States is actually on the decline.

When you look at the demographics of America’s prison population at first, it doesn’t look good for veterans. For example, about one in ten incarcerated people on death row have served in the military. This single statistic, however, only tells one side of the story. Overall, veterans are actually less likely than nonveterans to spend time in jail.

Between 2011 and 2012, only 8 percent of the total prison population were military veterans. This is a huge drop from a similar study conducted in 1978, when a solid 24 percent of all prisoners were veterans. The amount of vets committing crime has declined by two thirds in nearly 40 years, but why?

According to NPR, timing is everything. In 1978, the military population included millions aging heroes from World War II and conscripted troops from the Vietnam War. With much of the WWII generation gone and Vietnam War veterans entering their 70s, there are simply less veterans out there to commit crime.

Mental health also plays a role. Post-traumatic stress disorder wasn’t as well understood in the 70s as it is in the present day. Now, vets convicted of crimes can be sentenced to mental health counseling and therapy instead of jail.

Here are additional mental health statistics from the Bureau report:

About half of all veterans in prison (48 percent) and jail (55 percent) had ever been told by a mental health professional they had a mental disorder. Incarcerated veterans who saw combat were more likely than noncombat veterans to have ever been told they had a mental disorder. Veterans in prison and jail were more likely than nonveterans to report ever being told they had post-traumatic stress disorder (PTSD). Twice the proportion of veterans compared to nonveterans in prison (23 percent of veterans and 11 percent of nonveterans) and jail (31 percent of veterans and 15 percent of nonveterans) reported that a mental health professional had ever told them they had PTSD.