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Originally Posted by todd92
These numbers are all statisically identical. Even the stock plug had the same numbers...
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I agree. Completely.
I don't mean to be critical of the testing, but it's just not statistically valid. Not even close.
What he means is that in statistical analysis one has to take into consideration the run to run variation in the testing equipment itself as well as production variations in the product being tested, in this case the sparkplugs. When what seems to be gains falls within the run to run variation and the product production variation, they are phantom gains -- not real.
One must also eliminate all other variables that can influence the outcome. Testing must be done on the same machine, on the same day, with the same atmospheric conditions, including same engine operating temperatures, air density, temperature, humidity, etc.
For instance, you could compare eight different sets of spark plugs in this test.
They could actually be all the same brand and temperature rating. One of those sets would produce gains like the "best" in this test and one would produce power like the poorest . But since they all fall within the run to run variation of the dyno, the results are meaningless. This is also true in comparing plugs of different configurations from different manufacturers.
One reason: Most dynos cannot reliably get closer than 5 horsepower from one run to another. So, if you kept the same plugs in and made the same number of runs on the same dyno without changing the plugs at all, you'd see the same variations as reported in this test.
Now if you can show repeatable gains of 10 horses or greater, while eliminating all other variables, then there is a basis to claim that there is an improvement.
Measuring horsepower or torque on a dyno down to fractions of a horsepower and claiming this is accurate is, respectfully, pure fantasy.
Anyone here who has had their truck dynoed, is going to say that the run to run variation on the same truck on the same dyno on the same day, at the same temperature and humidity is highly likely to produce variations far larger than that found in these spark plug tests.
That's why multivariate statistical analysis is used in scientific research. You must eliminate as many variables as possible and identify and allow for the margin of error of the test equipment and production variations in the product.
This is also why tests which show differences in fuel mileage from one tested product to another will not be statistically valid unless all the other variables are eliminated -- changes in temperature, humidity, altitude, throttle position (heavy foot, light foot, going up hill down hill, vehicle weight variations, tire pressure -- the list goes on and on.
Designing tests that produce statistically valid results when the differences are small is very hard work.
Just one opinion.