ISW data show there have been 40 attacks this year, more than in the past four years combined.
The study says that the limited number of attacks makes it difficult to determine the cause of attacks.
The Pentagon has said a majority of insider attacks, or green-on-blue attacks, are due to personal disputes, but has acknowledged that a growing number are due to insurgent infiltration, up to as many as 25 percent this year.
“Insider attacks are a complex phenomenon, and the trends in the data do not demonstrate causality,” the authors write.
Insider attacks have become a major issue in the Afghan war as the number of Afghan troops and police have increased and NATO is readying the 2014 transition. U.S. and NATO troops are supposed to train their Afghan counterparts to take control of security by the end of 2014.
The rise in insider attacks led NATO to temporarily suspend some joint operations earlier this year, although they were resumed a few weeks later.
Read the full ISW study and maps here.