Teaching is highly educational for teachers. Teaching from the first edition revealed to us how much students enjoyed Monte Carlo methods, and the ability with such methods to test and to check every derivation, test, procedure or result in the book. Thus, a change in the second edition is to introduce Monte Carlo as early as possible (Chapter 2). Teaching also revealed to us areas in which we assumed too much (and too little). We have therefore aimed for some smoothing of learning gradients where slope changes have appeared to be too sudden. Chapters 6 and 7 substantially amplify our previous treatments of Bayesian hypothesis testing/modelling, and include much more on model choice and Markov chain Monte Carlo (MCMC) analysis. Our previous chapter on 2D (sky distribution) analysis has been significantly revised. We have added a final chapter sketching the application of statistics to some current areas of astrophysics and cosmology, including galaxy formation and large-scale structure, weak gravitational lensing, and the cosmological microwave background (CMB) radiation.

We received very helpful comments from anonymous referees whom CUP consulted about our proposals for the second edition. These reviewers requested that we keep the book (a) practical and (b) concise and – small, or ‘backpackable’, as one of them put it. We have additional colleagues to thank either for further discussions, finding errata or because we just plain missed them from our first edition list: Matthew Colless, Jim Condon, Mike Disney, Alan Heavens, Martin Hendry, Jim Moran, Douglas Scott, Robert Smith and Malte Tewes.