la loi de composition des variances

19:21 Jun 22, 2010
This question was closed without grading. Reason: Answer found elsewhere

French to English translations [PRO]
Science - Mathematics & Statistics / chemistry, metrology, chemometrics, measurement, uncertainty
French term or phrase: la loi de composition des variances
I work for a large industrial chemistry group, and I'm translating procedures relating to metrology and measurement uncertainty.

The term "loi de composition des variances" has come up several times now, and as yet I'm yet to come across a (verifiable/trustworthy/reliable) translation into English (my statistical knowledge is essentially nil). I've tried emailing a few experts in the field but as yet noone has come forward with an answer for me (apart from a couple of responses on another forum which I have been unable to check...). Anyone got any ideas ?
wsetters
Local time: 17:43


Summary of answers provided
4 +1Variance sum law
Tally Fenney
3variance decomposition/the law of total variance
liz askew
2law of combination of... errors?
SJLD
Summary of reference entries provided
liz askew

Discussion entries: 13





  

Answers


57 mins   confidence: Answerer confidence 3/5Answerer confidence 3/5
variance decomposition/the law of total variance


Explanation:
Based on the lack of convincing evidence for "la loi de composition des variances" in French, and my comments below and the evidence found on English sites re statistics.

Variance: Definition from Answers.com
In statistics, a variance is also called the mean squared error. .... This property is known as variance decomposition or the law of total variance and ...
www.answers.com/topic/variance-1 - Cached - Similar

liz askew
United Kingdom
Local time: 16:43
Native speaker of: Native in EnglishEnglish
PRO pts in category: 8
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2 hrs   confidence: Answerer confidence 4/5Answerer confidence 4/5 peer agreement (net): +1
Variance sum law


Explanation:
More generally, the variance sum law can be written as follows:

which is read "The variance of X plus or minus Y is equal the variance of X plus the variance of Y.
The formulas for the sum and difference of variables given above only apply when the variables are independent.



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Note added at 1 day2 hrs (2010-06-23 21:49:35 GMT)
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http://onlinestatbook.com/chapter3/variance_sum_law.html

Tally Fenney
United Kingdom
Local time: 16:43
Works in field
Native speaker of: French

Peer comments on this answer (and responses from the answerer)
agree  rkillings: cf. Wikipedia on the 'law of total variance': http://en.wikipedia.org/wiki/Law_of_total_variance
1 day 3 hrs
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1 day 3 hrs   confidence: Answerer confidence 2/5Answerer confidence 2/5
law of combination of... errors?


Explanation:
Routledge French dictionary of telecommunications: ... - Google Books ResultStuart Wittering - 1997 - Reference - 437 pages
... fibre d'injection/ law a GEN loi /; - of combination of errors TEST loi de composition des erreurs/ lay1; - perso nn GEN profane m ...
books.google.com/books?isbn=0415133483...

http://books.google.com/books?id=qqKgx47QMX8C&pg=PA113&lpg=P...

I won't go into the relationship between variance and error, but it is possible that this is what is meant. Impossible to know without more context.

SJLD
Local time: 17:43
Specializes in field
Native speaker of: Native in EnglishEnglish
PRO pts in category: 48
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Reference comments


39 mins
Reference

Reference information:
seriously

all I can find are refs. to "variance decomposition" and none with "variance composition":

http://www.google.co.uk/search?hl=en&lr=lang_en&as_qdr=all&t...

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Note added at 41 mins (2010-06-22 20:03:04 GMT)
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http://webcache.googleusercontent.com/search?q=cache:4NaukHb...


Il s'agit à contrario de toute technique d'évaluation non basée sur un procédé statistique. Une telle évaluation s'appuie généralement sur un jugement scientifique porté à la suite d'une analyse physique de la manipulation, utilisant toutes les informations disponibles. Il faut en particulier cerner la part d'incertitude qui est due à chacune des corrections associées aux causes d'erreur identifiées, même lorsqu'elles n'apportent pas à priori de dispersion aux résultats. On applique le même formalisme que pour les méthodes de type A, à savoir évaluer l'incertitude sur la correction (correction qui peut être nulle!) par une valeur Uj qu'on peut traiter comme un écart-type. Cette valeur est déterminée à partir d'éléments tels que bibliographie sur les matériaux et capteurs, notices des fournisseurs et constructeurs, certificats d'étalonnage, rapport d'intercomparaisons, ... mais aussi à partir des connaissances et du savoir faire de l'analyste et de l'opérateur. Cette manière de procéder revient, dans certains cas, à postuler l'existence sous-jacente d'une loi de distribution pour la correction considérée.
Pour obtenir l'incertitude Uc (écart-type) sur la correction totale, on applique la loi de composition des variances qui s'écrit, dans l'hypothèse où causes d'erreur et corrections sont non corrélées,




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Note added at 41 mins (2010-06-22 20:03:36 GMT)
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p.s.
if you open the last site you will actually find a formula at the bottom of the quoted text, which did not copy here...

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Note added at 44 mins (2010-06-22 20:06:25 GMT)
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BTW

although the above site states "loi de composition..." I have only found about 3 French hits for "loi de composition", the great majority of refs = loi de DEcomposition des variances:)

liz askew
United Kingdom
Native speaker of: Native in EnglishEnglish
PRO pts in category: 8
Note to reference poster
Asker: Hmm, I'd like to think it's decomposition, it would make my life a lot easier... It would certainly be logical. The frequency of the term and my boss' certainty that there is no other way to say it (she wrote the thing in the first place) suggest that it'd be a problematic assumption. I think I'm going to go digging in the standards documents the procedure is based on to see whether it'll clear things up...

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