“Almost all doctors carry the briefcase oui? And a man with a briefcase leaves Lord Tiddlewink’s room moments before he dies.” Poirot glared at Dr. Mutton.
“I don’t think that really-”.
“Damn you Poirot! I’d kill him again if I could!” The doctor yelled, interrupting Hastings.
“Oh, nevermind” sighed Hastings.
A base rate fallacy occurs whenever some inference is drawn on the basis of a probabilistic statement and complete set of evidence is not taken into account. So, for example, in the saga Poirot reasons that i) almost all doctors have a briefcase, ii) the killer had a briefcase and therefore iii) the killer is probably a doctor. Of course, this is faulty reasoning as it ignores how widespread briefcase ownership is: The proportion of doctors who own briefcases is very high, but the proportion of briefcase owners who are doctors is presumably very low (given that just about any professional could carry one). So the fact that the killer had a briefcase in no way implicates the doctor (at least not to any degree strong enough to base your case on).
Happily, as per usual Poirot’s gathering possible perpetrators into the same room and accusing one on them on the basis of some very weak evidence results in the murderer confessing their crime, so no harm done. That doesn’t make Hastings’ objection to Poirot’s reasoning any less right however.
I think I’ve done a much better job of drawing Hastings this time round (and yes I am shamelessly recycling earlier pictures of Poirot!) it looks a little more like Hugh Fraser and less like a man with a balloon that someone’s drawn a funny face on for a head. Let me know what you think.
Huzzah, a second saga for today! I’m clawing my way back to the right amount of sagas to days bit by bit. More sagas to come tomorrow, I;ve got some especially fun one’s lined up waiting to be illustrated so watch this space!