[Rdean58]

"Your method has you averaging the averages, which will give you an idea of the variances in individual measurements, but gives LESS accurate info on actual MPG's over the life of the car."

You are right, we are doing an average of averages. By doing it this way we get a more accurate representation of what the actual mileage may be.

We also get an idea of what the high & low mpg's will be. Using Statistical Analysis will allow us to monitor trends in the mileage of the car over it's lifetime.

For instance, if we discover a lowering of mpg over a period of time we know that something has changed. Whether or not it is the type/grade/quality of fuel we are using, the season we are driving in, heavier traffic, or perhaps a problem with the car.

Granted, a lot of this information could wind up to be useless (what are you going to do about the quality of the fuel?)

Also the more observations (fill ups) you have, the closer it will come to your Total Miles/Total Gallons used method.

It's basically another way of playing with the numbers and not getting too upset if your mileage falls down to 30.2 from a previous fillup of 34.5!

I've included some make believe fillups just to generate some numbers, check them out if you want. I used Excell to figure out my Standard Diviation.


Fillup # miles gallons MPG Average StdDev UCL LCL Total of MPG
1 350 11.5 30.4 30.4
2 360 11.2 32.1 31.3 1.2 32.5 30.1 62.6
3 275 8.9 30.9 31.2 0.9 32.0 30.3 93.5
4 265 8.2 32.3 31.4 0.9 32.4 30.5 125.8
5 298 9 33.1 31.8 1.1 32.9 30.7 158.9
6 255 7.9 32.3 31.9 1.0 32.9 30.9 191.2
7 152 5 30.4 31.7 1.1 32.7 30.6 221.6
8 417 12.6 33.1 31.8 1.1 32.9 30.7 254.7
9 420 13 32.3 31.9 1.1 32.9 30.8 287.0
10 398 12 33.2 32.0 1.1 33.1 30.9 320.2
11 368 11.6 31.7 32.0 1.0 33.0 31.0 351.9
12 358 11.5 31.1 31.9 1.0 32.9 30.9 383.0
13 401 12 33.4 32.0 1.0 33.1 31.0 416.4
14 412 11.4 36.1 32.3 1.5 33.8 30.8 452.6
15 115 3.6 31.9 32.3 1.4 33.7 30.9 484.5
16 410 11.9 34.5 32.4 1.5 33.9 30.9 519.0
17 398 11.6 34.3 32.5 1.5 34.1 31.0 553.3
18 397 11.9 33.4 32.6 1.5 34.1 31.1 586.6
19 396 12 33.0 32.6 1.4 34.1 31.2 619.6
20 365 12.3 29.7 32.5 1.5 34.0 30.9 649.3
21 325 12.7 25.6 32.1 2.1 34.3 30.0 674.9
22 395 12.2 32.4 32.1 2.1 34.2 30.1 707.3
23 375 11.7 32.1 32.1 2.0 34.2 30.1 739.3
24 396 10.9 36.3 32.3 2.2 34.5 30.2 775.7
25 427 13 32.8 32.3 2.1 34.5 30.2 808.5
Total 8728 269.6 32.4 (Average of all miles driving divided by all gallons used)
UCL = Upper Control Limit
LCL = Lower Control Limit
Thanks for reading