That's a tough one.
But not much tougher than proving that electronic throttle controls DIDN'T cause runaway cars -- even though there is not a whiff of proof that those controls ever have caused anybody to speed out of control.
In the absence of that negative proof, let's take a quick look at unintended acceleration.
Toyota got into trouble almost a year ago because, although it had more reports of unintended acceleration than did other automakers, it was very slow in responding to reports of runaway cars.
The company's reputation took a huge hit. Congress declared open season on Toyota.
Two actual problems have been identified: 1) in rare cases, floor mats can trap the accelerator pedal, and 2) some accelerator pedals have a tendency to stick. Toyota has recalled millions of cars.
What's the cause of most reports of unintended acceleration in Toyotas or anybody else's cars? Drivers who push on the gas pedal while thinking they're slamming on the brakes. (See Audi, 1980s.)
This doesn't mean Toyota shouldn't have dealt with the floor mats and sticky pedals years earlier.
But now that it's open season on Toyota, some members of Congress, some plaintiffs' attorneys, and some safety consultants argue that electronic throttle controls could be/may be/have to be the problem.
Toyota, which has some pretty good engineers, swears it can't find electronic gremlins. Now the National Highway Traffic Safety Administration reports that in cases where it studied the data recorders following accidents whose drivers blamed unintended acceleration, the drivers failed to brake at all or did so too late or while also stepping on the gas.
It's just a few dozen cases. But it's more evidence that … there is no evidence of an electronic problem.
The agency soberly concludes: "NHTSA officials have drawn no conclusions about additional causes of unintended acceleration in Toyotas beyond the two defects already known -- pedal entrapment and sticking gas pedals."
That's a pretty good summary. Martians may cause problems. So might electronic throttle controls. But absent a single piece of evidence, let's at least withhold judgment.