[Stoves] Sets of tests and the CoV of results - various methods

[Crispin Pemberton-Pigott]

Sorry about that



CoV Coefficient of Variation. It is the Standard Deviation (SD) divided by the Mean.



For example if the Mean (average) is 10 and the Standard Deviation is ±1 (also the value Sigma 1, "σ1") then the CoV is 1/10 = 0.1 x 100 = 10%



Both the mean and the standard deviation are directly related to the values in the data so to get a statement about how 'variable' the results were, the SD is divided by the mean turning the deviation into a fraction of the value. This is multiplied by 100 to get a % number.



The CoV for test results varies with the stove, the test protocol and the task completed during the test.



Something that is lacking from our conversation is the idea that some stoves are themselves variable in performance even if everything else is identical. The current analysis of results allows no room for product variability. I proposed that the Sigma one value be deducted from the mean before reporting the performance. This addresses issues related to the test method and the product, either of which may result in variation in the result.



The idea that a stove should be tested until the CoV meets a certain value ignores the possibility that the stove itself is simply a variable product. This is another misconception that has to be addressed by a future and acceptable international standard.



Regards

Crispin



-----Original Message-----
From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Andrew Heggie
Sent: 28-Jan-17 18:34
To: Discussion of biomass cooking stoves <stoves at lists.bioenergylists.org>
Subject: Re: [Stoves] Sets of tests and the CoV of results - various methods



Crispin am I the only one who stumbled over comprehending CoV probably meant covariance?



Andrew



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