## guesstimation (1+2)

I received very recently this book, Guesstimation 2.0, written by Lawrence Weinstein from Princeton University Press for review in CHANCE and decided to check the first (2008 )volume, Guesstimation, co-written by Lawrence Weinstein and John A. Adam. (Discovering in the process that they both had a daughter named Rachel, like my daughter!)

The title may be deemed to be very misleading for (unsuspecting) statisticians as, on the one hand, the book does not deal at all with estimation in our sense but with approximation to the right order of magnitude of an unknown quantity. It is thus closer to Innumeracy than to Statistics for Dummies, in that it tries to induce people to take the extra step of evaluating, even roughly, numerical amounts (rather than shying away from it or, worse, of trusting the experts!). For instance, how much area could we cover with the pizza boxes Americans use every year? About the area of New York City. (On the other hand, because Guesstimation forces the reader to quantify one’s guesses about a certain quantity, it has a flavour of prior elicitation and thus this guesstimation could well pass for prior estimation!)

To help with this reasoning and the recovery of (magnitude) numeracy, Lawrence Weinstein added an appendix called “Pegs to hang on” where he lists equivalent objects for a range of lengths, weights, etc. (The equivalent can be found in Guesstimation.) The books both start with a similar section on how to make crude evaluations by bounding the quantity and taking the geometric mean. I also like the way he battles for using metric units and powers of 10 in calculation, and join us in fighting against extra digits, claiming they are lies, not precision, which is true! Illustrating the point with the following xkcd strip:

A few problems in Guesstimation 2.0 irked me, including all related to recycling because they only gave the monetary gain in recycling a bottle, a can, etc., versus the time required for an individual to dump this object in the right bin: not the most constructive approach to recycling (see, instead, David McKay’s Sustainable Energy Without the Hot Air much more coherent evaluation). The same was true for the landfill question in Guesstimation: the volume of trash produced by Americans over 100 years may well fit in a 100m high hill over 10⁶ square meters, but landfills are definitely not the solution to garbage production! There are also one or two probability related problems: for instance the one about getting a baseball ball inside one’s beer glass during a game. Lawrence Weinstein goes from the probability of getting one foul ball being 3×10-4 to the probability of getting one of the forty foul balls during one game equal to 10 -2 without the beginning of an explanation. (This is true but how does he get there?!) I also found very amazing the computation that climbing 6 flights of stairs (what I usually do to get to my office in Paris-Dauphine, sometimes several times a day) consumes (roughly) 100W, which is twice an average daiily intake. Am I missing something? The relation does not seem right. (By the way, it seems question 7.10 did not make it to Guesstimation 2.0 as it reads as a quick intro to angular momentum, a recap usually found. at the start of a chapter.)