Quote:
Originally Posted by khafra
Thanks, InsightfulRay! Now, don't quote me on this to any statisticians; I asked one I know whether I can in good conscience give a confidence interval for an experiment with just three data points in each condition of the variable, and he laughed at me.
So, the airtabs dramatically increased the variance in your mpg 
(I can't think of a mechanism by which that would occur, unless they increased your susceptibility to crosswinds and one of those tanks was during a week of heavy winds).
Because of that big variance in the post-tab mpg, the distribution for the post-tab values is smeared out over a big range. If you could do three more fillups and post those numbers, we could probably get a much higher confidence.
*However*, according to Student's T-Test (which I picked because it's the easiest to use, not because it's the most appropriate here), there's only an 8.9% chance that nothing changed between these two distributions of numbers.
That's not good enough for journal publication, but if nothing changed besides the airtabs, that's pretty damned convincing to me. |
Wow, this is cool stuff even if I don't understand it.
I can attest that nothing else was changed but the airtabs so we can put that potential contamination to rest. I'll continue to forward consumption data as I accumulate it. I did another tank just recently but it was a great deal more city driving than I usually do hence lower MPG (44.5 to be exact). It would definitely skew things so I won't send you that one. I anticipate a fill-up later this coming week and the driving conditions are fairly typical of the 3 "post airtab" tanks I sent to you. I'm on an indicated 50.9 mpg as of now with about 200 miles on this tank.
So I see statistics can be fun — especially if you have someone else doing your analysis!
