When U.S. Defense Secretary Donald Rumsfeld referred to the "known unknowns" that remained in Iraq in 2002, he was mocked endlessly -- and those mysterious black holes ended up confounding his administration's project there. Rumsfeld's not the only one to encounter this epistemological puzzle: Known unknowns are everywhere, waiting to trip us up. Here are a few of the most enigmatic.
What we know we don't know: No one knows who exactly lives in Lebanon. The country hasn't held a census since the French colonial government conducted one in 1932.
Why we don't know it: A census would likely reveal the uncomfortable truth -- for Lebanon's Maronite Christians -- that their numbers have been slipping as a percentage of the population. When Lebanon became independent in 1943, a national pact divided power between Christians and Muslims on a 6-5 ratio based on the 1932 census, later changed to an even split after the country's brutal 1975-1990 civil war. Since then, the Shiite Muslim community is believed to have grown faster than any other group, but Christians, despite making up only an estimated quarter of the population, still hold half the parliamentary seats. They'd prefer to keep it that way.
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What we know we don't know: Even Nigeria's state oil company admits that it "cannot guarantee 100 percent accuracy" for its statistics on how much oil the country produces -- this in a state where oil generates more than 80 percent of government revenue.
Why we don't know it: Nigeria's oil sector is plagued by corruption and willful ignorance, and that extends to accounting. One watchdog group put the discrepancies in the Nigerian Central Bank's oil earnings figures at around $155 million for 2005. With Western oil majors heavily invested in the Niger Delta, there's suspicion that those companies are extracting more than they're reporting. The unrest in the oil-rich delta has also played a role in the uncertainty, with hundreds of thousands of barrels thought to have been lost since the early 1990s due to sabotage by rebel groups.
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What we know we don't know: No one has ever really been sure how much fissile material Russia has -- possibly not even Russia itself -- except that it's more than anyone else's and some of it has likely gone missing.
Why we don't know it: After the breakup of the Soviet Union, the country's nuclear infrastructure was consolidated into facilities within Russia, often with lax security and accounting procedures. Accounting has since improved, and the country is now thought to have around 145 metric tons of weapons-grade plutonium. But with more than 140 nuclear reactors of varying levels of security throughout the country, many analysts think it's a near-certainty that some has slipped through the cracks.
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HAITI'S DEATH TOLL
What we know we don't know: Estimates of the victims claimed by Haiti's devastating Jan. 12 earthquake range from President René Préval's 300,000 to the "well under 100,000" put forth by a skeptical Dutch news agency. The big round numbers should be a hint that no one really has any idea.
Why we don't know it: Death-toll numbers frequently swing wildly for a few weeks after natural disasters. But in Haiti, where an unstable government had little grasp of the country's population under the best of circumstances, the challenge was far greater. The lack of resources also meant that most attention was paid to the living, while dead bodies were often disposed of haphazardly with little documentation. Some citizens have even accused the government of deliberately inflating casualty numbers to attract more foreign aid.
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