WASHINGTON: Acquisition experts agree that accurate cost estimates can be devilishly difficult to get right. The Pentagon’s top cost estimator, Christine Fox, says current cost estimates are often accurate within several percentage points. That’s impressive, but on programs measured in the tens or hundreds of billions of dollars, a few percentage points can mean a few billion dollars.

Case in point: the F-35 Joint Strike Fighter. Its cost estimates have wandered between $1.1 trillion and $1.5 trillion just in the last year;that’s a $400 billiondifference. Now, that estimate assumes the F-35 flies for more than half a century (55 years) and makes all sorts of highly questionable assumptions, like the rate of inflation, the price of fuel, labor costs and on and on.

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