**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!)

**T**he 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!)

**I**n about 80 questions, Lawrence Weinstein [with John A. Adam in *Guesstimation*] explains how to roughly “estimate”, i.e. guess, quantities that seem beyond a layman’s reach. Not all questions are interesting, in fact I would argue they are mostly uninteresting *per se* (e.g., what is the surface of toilet paper used in the U.S.A. over one year? how much could a 1km meteorite impacting the Earth change the length of the day? How many cosmic rays would have passed through a 30 million-year-old bacterium?), as well as very much centred on U.S. idiosyncrasies (i.e., money, food, cars, and cataclysms), and some clearly require more background in physics or mechanics than you could expect from the layman (e.g., the energy of the Sun or of a photon, *P=mgh/t*, *L=mvr* (angular momentum), neutrino enery depletion, microwave wavelength, etc. At least the book does not shy away from formulas!) So *Guesstimation* and *Guesstimation 2.0 *do not make for a good bedtime read or even for a pleasant linear read. Except between two metro stations. Or when flying to Des Moines next to a drunk woman… However, they provide a large source of diverse examples useful when you teach your kids about sizes and magnitudes (it took me years to convince Rachel that 1 cubic meter was the same as 1000 liters!, she now keeps a post-it over her desk with this equation!), your students about quick and dirty computing, or anyone about their ability to look critically at figures provided in the newsy, the local journal, or the global politician. Or when you suddenly wonder about the energy produced by a Sun made of… gerbils! (This is Problem 8.5 in *Guesstimation* and the answer is as mind-boggling as the question!) Continue reading