## Computational Statistics

Do not resort to Monte Carlo methods unnecessarily.

**W**hen I received this 2009 Springer-Verlag book, ** Computational Statistics**, by James Gentle a while ago, I briefly took a look at the table of contents and decided to have a better look later… Now that I have gone through the whole book, I can write a short review on its scope and contents (to be submitted). Despite its title, the book aims at covering

*both*computational statistics and statistical computing. (With 752 pages at his disposal, Gentle can afford to do

*both*indeed!)

**T**he book ** Computational Statistics** is separated into four parts:

- Part I:
**Mathematical and statistical preliminaries**. - Part II:
**Statistical Computing**(Computer storage and arithmetic.- Algorithms and programming.- Approximation of functions and numerical quadrature.- Numerical linear algebra.- Solution of nonlinear equations and optimization.- Generation of random numbers.) - Part III:
**Methods of Computational Statistics**(Graphical methods in computational statistics.- Tools for identification of structure in data.- Estimation of functions.- Monte Carlo methods for statistical inference.- Data randomization, partitioning, and augmentation.- Bootstrap methods.) - Part IV:
**Exploring Data Density and Relationship**(Estimation of probability density functions using parametric models.- Nonparametric estimation of probability density functions.- Statistical learning and data mining.- Statistical models of dependencies.)

Computational inference, together with exact inference and asymptotic inference, is an important component of statistical methods.

**T**he first part of ** Computational Statistics **is indeed a preliminary containing essentials of math and probability and statistics. A reader unfamiliar with too many topics within this chapter should first consider improving his or her background in the corresponding area! This is a rather large chapter, with 82 pages, and it should not be extremely useful to readers, except to signal deficiencies in their background, as noted above. Given this purpose, I am not certain the selected exercises of this chapter are necessary (especially when considering that some involve tools introduced much later in the book).

The form of a mathematical expression and the way the expression should be evaluated in actual practice may be quite different .

**T**he second part of ** Computational Statistics **is truly about computing, meaning the theory of computation, i.e. of using computers for numerical approximation, with discussions about the representation of numbers in computers, approximation errors, and of course random number generators. While I judge George Fishman’s

*to provide a deeper and more complete coverage of those topics, I appreciate the need for reminding our students of those hardware subtleties as they often seem unaware of them, despite their advanced computer skills. This second part is thus a crash course of 250 pages on numerical methods (like function approximations by basis functions and …) and on random generators, i.e. cover the same ground as Gentle’s earlier books,*

**Monte Carlo***and*

**Random Number Generation and Monte Carlo Methods****, while the more recent**

*Numerical Linear Algebra for Applications in Statistics***looks very much like a shorter entry on the same topics as those of Parts III IV of**

*Elements of Computational Statistics***. This part could certainly sustain a whole semester undergraduate course while only advanced graduate students could be expected to gain from a self-study of those topics. It is nonetheless the most coherent and attractive part of the book. It constitutes a must-read for all students and researchers engaging into any kind of serious programming. Obviously, some notions are introduced a bit too superficially, given the scope of this section (as for instance Monte Carlo methods, in particular MCMC techniques that are introduced in less than six pages), but I came to realise this is the point of the book, which provides an entry into “all” necessary topics, along with links to the relevant literature (if missing**

*Computational Statistics**!). I however deplore that the important issue of Monte Carlo experiments, whose construction is often a hardship for students, is postponed till the 100 page long appendix. (I suspect that*

**Monte Carlo Statistical Methods***students do not read appendices*is another of those folk theorems!)

Monte Carlo methods differ from other methods of numerical analysis in yielding anestimaterather than anapproximation.

**T**he third and fourth parts of the book cover methods of computational statistics, including Monte Carlo methods, randomization and cross validation, the bootstrap, probability density estimation, and statistical learning. Unfortunately, I find the level of Part III to be quite uneven, where all chapters are short and rather superficial because they try to be all-encompassing. (For instance, Chapter 8 includes two pages on the RGB colour coding.) Part IV does a better job of presenting machine learning techniques, if not with the thoroughness of Hastie et al.’s ** The Elements of Statistical Learning: Data Mining, Inference, and Prediction**… It seems to me that the relevant sections of Part III would have fitted better where they belong in Part IV. For instance, Chapter 10 on estimation of functions only covers the evaluation of estimators of functions, postponing the construction of those estimators till Chapter 15. Jackknife is introduced on its own in Chapter 12 (not that I find this introduction ultimately necessary) without the bootstrap covered in eight pages in Chapter 13 (bootstrap for non-iid data is dismissed rather quickly, given the current research in the area). The first chapter of Part IV covers some (non-Bayesian) estimation approaches for parametric families, but I find this chapter somehow superfluous as it does not belong to the computational statistic domain (except as an

*approximation*method, as stressed in Section 14.4). While Chapter 16 is a valuable entry on clustering and data-analysis tools like PCA, the final section on high dimensions feels out of context (and mentioning the curse of dimensionality only that close to the end of the book does not seem appropriate). Chapter 17 on dependent data is missing the rich literature on graphical models and their use in the determination of dependence structures.

Programming is the best way to learn programming (read that again) .

**I**n conclusion, ** Computational Statistics** is a very diverse book that can be used at several levels as textbook, as well as a reference for researchers (even if as an entry towards further and deeper references). The book is well-written, in a lively and personal style. (I however object to the reduction of the notion of

*Markov chains*to discrete state-spaces!) There is no requirement for a specific programming language, although R is introduced in a somewhat dismissive way (R

*most serious flaw is usually lack of robustness*since

*some [packages] are not of high-quality*) and some exercises start with

*Design and write either a C or a Fortran subroutine*.

**BUGS**is not mentioned at all. The appendices of

**also contain the solutions to some exercises, even though the level of detail is highly variable, from one word (“1”) to one page (see, e.g., Exercise 11.4). The 20 page list of references is preceded by a few pages on available journals and webpages, which could get obsolete rather quickly. Despite the reservations raised above about some parts of**

*Computational Statistics***that would benefit from a deeper coverage, I think this book is a reference book that should appear in the shortlist of any computational statistics/statistical computing graduate course as well as on the shelves of any researcher supporting his or her statistical practice with a significant dose of computing backup.**

*Computational Statistics*
May 10, 2010 at 12:47 am

Anyone who recommends learning computational statistics by coding everything in C or FORTRAN is wasting everyone’s time. Don’t get me wrong, I use lots of FORTRAN code in my own work because its fast, but it is not a learning tool, and its a bear to work with day-to-day. Do yourself a favor: pick a high-level language like R or Python, and get good at it. Presumably you want to think about statistical problems, and not fiddly computing issues like memory management. Its not 1977 anymore, James Gentle.

May 10, 2010 at 6:31 am

Chris:Fortran is fast. Although I have not done anything in Fortran since the early 1980’s (!), I have a close colleague who moved back to Fortran lately, because he could not achieve the scale of experimentation he wanted with R. I agree that for learning computational statistics as in Gentle’s book, R is a softer entry, but there are real problems that only compiled languages can deal with, no matter how unfriendly they may be…