However, unsolved technical and design challenges made it impossible for NASA to provide a credible estimate.

Though top speed was the same as the Enzo's, 217 mph, Ferrari cited a credible 0-60 estimate of 2.8 seconds, a half-second quicker than the road car.

When taken as a whole, the participation rate for students with disabilities is sufficient to provide statistically credible estimates.

Probably the most credible estimate of the economic costs of smoking comes from the Congressional Office of Technology Assessment.

Dr. Woloshin said the most credible estimate is 3 percent.

And that toll ($19 billion a year by one credible estimate) is shouldered by all citizens, though far fewer than half actually have a car.

Rummel goes on to collate what he considers the most credible estimates published by others into what he calls democide.

Reliable statistics are lacking, but credible estimates suggest that tens of thousands of people have already died.

There were no credible estimates as to the number of mahadjirin children.