A report released in June from the Pew Research Center concluded that only 42% of Mexican immigrants eligible to become U.S. citizens actually applied and obtained citizenship in 2015. That percentage, according to Pew, is “one of the lowest among all immigrant groups when it comes to country of origin.”

The 42% naturalization rate is close to 30 points lower than the 74% naturalization rate for non-Mexican immigrant groups. The rate for Mexican naturalizations has remained steady since 2005, when the rate was at 38%. In 1995, that rate was at 20%.

“Overall, 11.9 million of the nation’s 45 million immigrants in 2015 held lawful permanent residence (LPR) status – that is, they held ‘green cards,’ according to Pew Research Center estimates,” Pew’s Ana Gonzalez-Barrera wrote about the findings. “Of this number, most (9.3 million) had met the eligibility requirements –including length of residence– to apply for U.S. citizenship in 2015. Mexicans made up 37% of this group and constituted the single largest group of green-card holders without U.S. citizenship by country of origin.”

In addition, Gonzalez-Barrera noted, “as of 2015, the naturalization rate for lawful Mexican immigrants trailed that of green-card holders from the Middle East by 42 percentage points (42% vs. 83%), and was 33 points behind green-card holders from Africa, 74% of whom had naturalized by 2015.”

The Pew study also explored the barriers to naturalization for Mexican immigrants. More than a third said it was due to “language and other personal barriers,” while 31% said they “have not tried yet or” were “not interested.”

The full Pew report is here.