It also said, however, that this does not necessarily indicate a causal relationship.

“Those in favor of dialogue with North Korea might see this as evidence of the efficacy of diplomacy,” the think tank said in its newsletter, “Beyond Parallel.”

“Skeptics will argue that the absence of North Korean provocations does not necessarily mean that nuclear proliferation, both horizontal and vertical, is not still occurring during these periods,” it added.

Still, diplomacy appeared to have a restraining effect on the frequency of provocations.

In the period between January 1993 and July 1994, the US and North Korea held 19 negotiation events over the regime’s nuclear weapons program. Pyongyang also carried out three provocations with short- to medium-range missile tests. The ratio of negotiations to provocations was highest at 6.3:1.

On the other hand, there have been no official nuclear negotiations since US President Donald Trump took office in January. North Korea has also conducted at least 24 missile tests and one nuclear test in the period between February and September, reducing the ratio to zero.

The ratio was highest under North Korea’s founding leader Kim Il-sung from 1990-94, and lowest under current leader Kim Jong-un from 2012 to the present.

The study also found no correlation between whether the US president is a Democrat or Republican and the pace of North Korean provocations.

“At the current pace, North Korea may do well over 100 missile tests during the four-year term of the US president, which would represent a historic high,” it said.

Tensions have escalated amid of war of words between Trump and Kim.

US Secretary of Rex Tillerson said Saturday that Washington maintains direct channels of communication with Pyongyang. Trump shot down the remark a day later, saying Tillerson is “wasting his time trying to negotiate with Little Rocket Man,” a reference to Kim.