I posted this at the Prius section about a month ago - when someone else got bent out of shape about the same thing. Even if several "bashers" or "false hypermilers" posted to one model, the median would not move more than 0.1mpg. I like medians - they resist outliers...

What might be cool is if the dbase could show mpg trends over time by model. A median chart with monthly buckets would be nice!

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The database does pull the median (50% tile) of the owners averages. I ran a stats test in Minitab using the dbase. The results do show that there is a statistically significant difference in the median mpgs posted. Prius is higher by +1.40 mpg with a confidence interval of +0.90 to +2.00 mpg. Is this a practical significance - probably not. This dbase is a subset of hybrid owners who have found this site and have posted their mileage data.

Both vehicles seem to suck a little (gas), though the Prius appears to suck less.

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Mann-Whitney Test and CI: MPG Prius, MPG HCH

N Median
MPG Prius 1155 47.500
MPG HCH 492 46.050


Point estimate for ETA1-ETA2 is 1.400
95.0 Percent CI for ETA1-ETA2 is (0.900,2.000)
W = 998602.0
Test of ETA1 = ETA2 vs ETA1 not = ETA2 is significant at 0.0000
The test is significant at 0.0000 (adjusted for ties)

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Also interesting is the fact that there are 19 Priuses at 47.5 today (5/15/07 - of the 1155), so the median may be pretty insensitive to changes at high/low extremes - even new ones. There are about 6 HCHIIs at their median.