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> Again, this assumes both that there were no errors made in the experiment This is worth repeating a lot when explaining sigma (even in a great and comprehens
by anyfoo 6y ago
> Again, this assumes both that there were no errors made in the experiment
This is worth repeating a lot when explaining sigma (even in a great and comprehensive explanation such as yours): Statistical anomalies are only relevant when the experiment itself is sound.
Imagine you are trying to see whether two brands of cake mix have different density (maybe you want to get a good initial idea whether they could be the same cake mix). You can do this by weighing the same amount (volume) of cake mix repeatedly, and comparing the mean value for weight measurements of either brand. That works well, but it totally breaks down if you consistently use a glass bowl for one brand, and a steel bowl for the other brand. You will get very high units of sigma, but not because of the cake mix.
- a1369209993 6y agoNitpick: it assumes that there were no systematic errors. If (say) you switch randomly between steel and glass bowls, you results will still be valid, just with much wider (worse) standard deviation than you could have gotten otherwise (or much greater numbers of measurements needed for a given accuracy, due to Shannon/noise floor issues).
- anyfoo 6y agoYes, that's entirely my point, hence why I said "consistently" using one type of bowl for one brand. That's a systematic error, but since this was supposed to be educational, I preferred explaining the error instead of using terminology that basically implies knowledge already.