Data is taken since 6/2003. Visits to the same station were grouped together, couple outliers were excluded (one 38.8 MPG data point - the tank consisted of almost entirely downhill miles 8000' to sea level). I go to shell for the 5% rebate on gas since 10/03 whenever is possible.
Y error bars are +/- the standard deviation and as you can see, they all overlap. Therefore I cannot find any statistical difference between these gas stations that I use. It elimates one variable when comparing MPG tank by tank, at least.
Data:
average MPG | std dev | #samples
exxon | 33.14 | 0.90 |12
shell #1 | 33.52 | 1.54 | 15
shell #2 | 33.19 | 0.84 | 12
shell #3 | 34.07 | 1.06 | 55
shell #4 | 33.59 | 1.25 | 9
shell #5 | 34.18 | 0.92 | 12
vons gas | 34.12 | 0.81 | 7
Y error bars are +/- the standard deviation and as you can see, they all overlap. Therefore I cannot find any statistical difference between these gas stations that I use. It elimates one variable when comparing MPG tank by tank, at least.
Data:
average MPG | std dev | #samples
exxon | 33.14 | 0.90 |12
shell #1 | 33.52 | 1.54 | 15
shell #2 | 33.19 | 0.84 | 12
shell #3 | 34.07 | 1.06 | 55
shell #4 | 33.59 | 1.25 | 9
shell #5 | 34.18 | 0.92 | 12
vons gas | 34.12 | 0.81 | 7