Re: [SystemSafety] Practical Statistical Evaluation of Critical Software

From: Derek M Jones < >
Date: Sun, 01 Mar 2015 18:21:26 +0000


Lets apply a well known adage:
"All models are wrong but some are useful".

Lets put to one side the extent to which the proposed model is wrong.

I don't see how the proposed model is useful.

The use of Bernoulli/Poisson mathematics is proposed and you correctly point out that this only works if the data has the desired properties.

I would have proposed any combination of distributions, said the same thing and been just as correct as you.

Surely the approach should be to tell engineers to find out what distribution(s) their data has and then apply the probability analysis appropriate to that distribution(s)?

> As I mentioned last week, Bev Littlewood and I have been writing a short practical guide to
> statistical evaluation of software with high-reliability requirements. It has been apparent to us
> for a while that IEC 61508-7 Annex D is an insufficient and in some respects misleading guide to the
> statistical evaluation of critical software, and it's been there in the standard by now for 18
> years. Time to fix that. This is the material we think should go into a revision.
> It's available at and has
> also been submitted for publication.
> Prof. Peter Bernard Ladkin, Faculty of Technology, University of Bielefeld, 33594 Bielefeld, Germany
> Je suis Charlie
> Tel+msg +49 (0)521 880 7319
> _______________________________________________
> The System Safety Mailing List
> systemsafety_at_xxxxxx >

Derek M. Jones           Software analysis
tel: +44 (0)1252 520667
The System Safety Mailing List
Received on Sun Mar 01 2015 - 19:21:51 CET

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