Petty theft

Suppose that we have an on-going series of thefts of petty cash from a drawer holding our  tea-club funds. We note that the money only ever goes missing when a particular security guard is on duty overnight. A clear case of cause and effect!

But now suppose that the money only ever goes missing when both of two particular security guards are on duty. Again, we could assign some aspect of causality to both. What are the associated likelihoods/probabilities/weights of evidence?

Both are searched at the end of their next shift, but have no change. What now?

Now suppose we realise that there is a cigarette vending machine available, and only one of the suspects smokes. What now?

Some of my thinking follows …

.

.

.

.

.

.

.

.

.

.

If you’ve looked at the rst of my blog you might realise that there three ways you might tackle these questions:

  1. What do I think?
  2. What would a naïve application of ‘received wisdom’ (e.g., as routinely taught to bidding scientists and widely practised).
  3. Where would taking the underlying logic/mathematics (as distinct from pseudo-mathematics) seriously get you?
  4. What do you think now?

Hence, the whole point of the blog: is there a difference between (2)and (3) and does it matter? I tend to think that it does, and that an improvement on (2) would be to provide some good pedagogic examples, of which this is an attempt. For now, I leave a worked example of (3) for the reader, on the grounds that this is much less important than appreciating the limitations of (2). I would be happy to comment on readers ideas, though.

 

Dave Marsay

 

Advertisements
%d bloggers like this: