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mncoppola / ChronoPlotter

Easily generate graphs using recorded data from LabRadar, MagnetoSpeed, and ProChrono chronographs and ShotMarker e-target
MIT License
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STDEV.S function v STDEV.P function #3

Closed jcampbellsmith closed 2 years ago

jcampbellsmith commented 2 years ago

I ran ChronoPlotter today on some data I collected this morning. In Excel I only use the STDEV.P function and this gives me a lower SD than the ChronoPlotter calculation.

The STDEV. P function is used when your data represents the entire population. The STDEV. S function is used when your data is a sample of the entire population.

.pdf shows my data entry. Extract page.pdf Excel shows my own calculation. Book1.xlsx

mncoppola commented 2 years ago

Hi, the sample standard deviation (STDEV.S) is the proper calculation to use in this instance. The population stdev should only be used if we've collected every shot the rifle has ever and can ever shoot. In our case we're collecting a smaller sample of shots looking to estimate what future shots will do, so we need to use the sample stdev.

https://stats.stackexchange.com/questions/485326/confused-when-to-use-population-vs-sample-standard-deviation-in-engineering-test/485355#485355

If you re-calculate with STDEV.S the numbers should agree with ChronoPlotter