The researchers found that a record increase in restrictions on religion have been imposed by many governments around the world, with Christians facing harassment in 143 countries.
Release International, which supports persecuted Christians around the world, said while it "welcomes the report", it didn't paint an entirely accurate picture of global Christian persecution.
"The sheer breadth of their investigation means it is behind the times," a statement from the charity states.
"From our own findings, we would say that insufficient emphasis is placed on the growing restrictions in China and the severe persecution of Christians in North Korea."
Release International said the persecution level in China is even higher than this research reveals as the research stops at 2017.
"The following year, China imposed even tougher new restrictions to clamp down on Christians in their country," Paul Robinson from the charity explained.
China has also restricted the number of religious groups who can register with the government to hold worship services.
However, there are reports that even registered Christian churches are being shut down by the government. North Korea isn't included at all in the Pew report.
The explanation given reads: "Primary sources indicate that the North Korean government is among the most repressive in the world, including toward religion.
"But because independent observers lack regular access to North Korea, the sources are unable to provide the kind of specific, timely information that forms the basis of this report."
Release International contributed to the research led by the Bishop of Truro on Christian persecution that has now been accepted by the government.
Stay up to date with the latest news stories from a Christian perspective. Sign up to our daily newsletter and receive more stories like this straight to your inbox every morning.
