A Trump presidency in the wings who’d have thought! And what a total shock it was to all those pollsters, commentators and apparatchiks who are now trying to explain why they got it so wrong. All of which is a textbook example of what students of risk theory call a Black Swan event. Continue Reading…
An Outside Context Problem was the sort of thing most civilisations encountered just once, and which they tended to encounter rather in the same way a sentence encountered a full stop.
More infernal statistics
Well, here we are again. Given recent developments in the infernal region it seems like a good time for another post. Have you ever, dear reader, been faced with the problem of how to achieve an unachievable safety target? Well worry no longer! Herewith is Screwtape’s patented man based mitigation medicine.
The first thing we do is introduce the concept of ‘mitigation’, ah what a beautiful word that is. You see it’s saying that it’s OK that your system doesn’t meet its safety target, because you can claim credit for the action of an external mitigator in the environment. Probability wise if the probability of an accident is P_a then P_a equals the product of your systems failure probability P_s and. the probability that some external mitigation also fails P_m or P_a = P_s X P_m.
So let’s use operator intervention as our mitigator, lovely and vague. But how to come up with a low enough P_m? Easy, we just look at the accident rate that has occurred for this or a like system and assume that these were due to operator mitigation being unsuccessful. Voila, we get our really small numbers.
Now, an alert reader might point out that this is totally bogus and that P_m is actually the likelihood of operator failure when the system fails. Operators failing, as those pestilential authors of the WASH1400 study have pointed out, is actually quite likely. But I say, if your customer is so observant and on the ball then clearly you are not doing your job right. Try harder or I may eat your soul, yum yum.
Never confuse volume with authority.
A clank of botnets
More bad news for the Internet this week as a plague of BotNets launched a successful wave of denial of service attacks on Dyn, a dynamic domain name service provider. The attacks on Dyn propagated through to services such as Twitter (OK no great loss), Github, The Verge, Playstation Network, Box and Wix. Continue Reading…
Well hello there, it’s been a while hasn’t it?
In the absence of our good host I thought I’d just pop in and offer some advice on how to use statistics for requirements compliance. Now of course what I mean by requirements compliance is that ticklish situation where the customer has you over the proverbial barrel with an eye-gouger of a requirement. What to do, what to do. Well dear reader all is not lost, what one can do is subtly rework the requirement right in front of the customer without them even recognising it…
No! I hear you say, ‘how can this wonder be achieved Screwtape?’
Well it’s really quite simple, when one understands that requirements are to a greater or lesser extent ‘operationally’ defined by their method of verification. That means that just as requirements belong to the customer so too should the method one uses to demonstrate that you’ve met them. Now if you’re in luck the customer doesn’t realise this, so you propose adopting a statistical proof of compliance, throw in some weaselling about process variability, based on the median of a sample of tests. Using the median is important as it’s more resistant to outlier values, which is what we want to obfuscate (obviously). As the method of verification defines the requirement all of a sudden you’ve taken the customer’s deterministic requirement and turned it into a weaker probabilistic one. Even better you now have psychological control over half of the requirement, ah the beauty of psychological framing effects.
Now if you’ll excuse me all this talk of statistics has reminded me that I have some souls to reap over at the Australian Bureau of Statistics*.Mmm, those statisticians, their souls are so dry and filled with tannin, just like a fine pinot noir.
Till the next time. Yours infernally,
*Downstairs senior management were not amused by having to fill out their name and then having a census checker turn up on their doorstep asking whether they were having a lend of the ABS.