[SystemSafety] Comparing reliability predictions with reality

[Prof. Dr. Peter Bernard Ladkin]

On 2025-02-26 16:42 , Gareth Lock wrote:
> Scott Snook’s ‘Friendly Fire’ is a great book on this topic.

I have my problems with a lot of what Snook says in the book.

First, his causal analysis is hopeless. See https://rvs-bi.de/publications/Reports/ladkin-SCS03.pdf 
(an invitedpaper, in*Safety Critical Systems and Software 2003*, the Proceedings of the 8th 
Australian Workshop on Safety Critical Software and Systems, volume 33 of/Conferences in Research 
and Practice in Information Technology/, ed. Peter Lindsay and Tony Cant, Australian Computer 
Society, 2004).

Second, he used Jens Rasmussen's notion of "Migration to the Boundary" centrally, without crediting 
Rasmussen.See Rasmussen, J., Risk Management in a Dynamic Society: A Modelling Problem, Safety 
Science 27(2/3), 1997). He observed that people working in a complex sociotechnical system will 
often “optimise” their tasks to make them “easier”, or even in some cases he observed to make them 
doable at all. That means the tasks are not performed according to the organisational intent. 
Rasmussen noted that this happens almost invariably; he was just the first to put a name to it.

One thing on which Nancy Leveson and I agreed (yes, there were some such things!) was our view of 
Snook's analysis.

PBL

Prof. Dr. Peter Bernard Ladkin
Causalis Limited/Causalis IngenieurGmbH, Bielefeld, Germany
Tel: +49 (0)521 3 29 31 00