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Why Counts Of Islamic State Fighters Are So Uncertain

Islamic State, the extremist group in the Middle East that U.S. President Barack Obama has pledged to defeat, is adding fighters quickly, according to the CIA. Last week, the Central Intelligence Agency reported that the group’s numbers have risen to between 20,000 and 31,500 fighters across Iraq and Syria. That’s at least double the intelligence agency’s prior estimate of 10,000 fighters. The new estimate was widely reported, often with the word “triple” in the headline, reflecting the upper end of the range.

How does the CIA count fighters in Islamic State, a group — also referred to as ISIS or ISIL — not likely to answer a survey or publish a roster? A CIA spokesman provided about as much detail as you’d expect. The estimate is “based on a new review of all-source intelligence reports from May to August,” spokesman Ryan Trapani said in an email. He attributed the group’s growth to “stronger recruitment since June following battlefield successes and the declaration of a caliphate, greater battlefield activity, and additional intelligence.”

Intelligence experts outside the CIA cast some doubt on the precision of the estimate. Michael O’Hanlon, a senior fellow at the Brookings Institution, a centrist think tank in Washington, said even the wide range of numbers may understate the uncertainty in the count. “I’d say the estimates are no better than +/- 50%,” O’Hanlon said in an email.

Anne Stenersen, a research fellow at the Norwegian Defence Research Establishment in Kjeller, Norway, said the accuracy of the estimates depends on the CIA’s sources. “For a country like Afghanistan, I would trust their estimates because they have access to many different sources on the ground,” Stenersen said in an email. “In Iraq/Syria and for a group like ISIS, it is really hard to know where they get their numbers from, and how reliable they are.”

John Arquilla, professor of defense analysis at the Naval Postgraduate School in Monterrey, California, said the apparent doubling or tripling of fighters might reflect new methodology rather than an actual surge numbers. “When you have a rapid doubling or tripling of estimates, it is almost always associated with a new way of counting,” Arquilla said. “In this case, my guess is that groups with tight kinship ties to known fighters are being included in the count, whereas the first core estimates of front-line fighters may not have cast the net this widely.”

O’Hanlon also guessed at how the CIA might be counting: “They might find what they think is a typical cell and then try to estimate how many cells based on geographic reach, or signals intelligence” — listening to cellphones or satellite phones. It is, he said, “very hard to count people this way.”

People aren’t necessarily the most relevant indicator of group strength, anyway. “We didn’t even try” to count people in the Cold War, O’Hanlon said, “when we already had good satellites — we preferred to count Russian tanks, bombers, and ICBMs, not soldiers.”

“Numbers tell us something about the group’s strength, but not everything,” Stenersen said. “It depends what threat you are looking at. Numbers are important to conquer and hold territory, but level of training, and access to heavy weapons, is also important. For international terrorism against the West, you don’t need great numbers if you have a leadership who is dedicated to carry out such attacks, and a few willing recruits.”

Carl Bialik was FiveThirtyEight’s lead writer for news.