Who's a good mathematician/statistician?

[theclencher]

I'm wondering how many miles should be accrued/gallons consumed before a statistically accurate FE value can be derived?

Certainly one mile isn't enough, and 100,000 miles is more than enough.

Certainly one cup of gas isn't enough, and 1,000 gallons is more than enough.

It's somewhere in between. Maybe it's not a single value?

Super High Mileage competitions perhaps can get away with a smaller miles/gallons sample due to their extreme efforts at measuring accuracy...? If they claim 10,000 mpg, what does that mean? I'm pretty sure if they were given one gallon of fuel they wouldn't be able to go 10,000 miles...? But then they don't have the luxury of dragging the competition out for days or weeks. Did VW use a good enough sample for their 1L claim- one trip? If someone "hypermiles" a Hummer for a specific trip segment and gets 15 instead of 10, yet a 90-day gaslog shows 10, what does that mean? Is the 90-day interval accurate?

Inquiring minds want to know...