# Statistical Thinking for the 21st Century

*Draft: 2022-02-26*

# Preface

The goal of this book is to the tell the story of statistics as it is used today by researchers around the world. It’s a different story than the one told in most introductory statistics books, which focus on teaching how to use a set of tools to achieve very specific goals. This book focuses on understanding the basic ideas of *statistical thinking* — a systematic way of thinking about how we describe the world and use data make decisions and predictions, all in the context of the inherent uncertainty that exists in the real world. It also brings to bear current methods that have only become feasible in light of the amazing increases in computational power that have happened in the last few decades. Analyses that would have taken years in the 1950’s can now be completed in a few seconds on a standard laptop computer, and this power unleashes the ability to use computer simulation to ask questions in new and powerful ways.

The book is also written in the wake of the reproducibility crisis that has engulfed many areas of science since 2010. One of the important roots of this crisis is found in the way that statistical hypothesis testing has been used (and abused) by researchers (as I detail in the final chapter of the book), and this ties directly back to statistical education. Thus, a goal of the book is to highlight the ways in which current statistical methods may be problematic, and to suggest alternatives.

## 0.1 Why does this book exist?

In 2018 I began teaching an undergraduate statistics course at Stanford (Psych 10/Stats 60). I had never taught statistics before, and this was a chance to shake things up. I have been increasingly unhappy with undergraduate statistics education in psychology, and I wanted to bring a number of new ideas and approaches to the class. In particular, I wanted to bring to bear the approaches that are increasingly used in real statistical practice in the 21st century. As Brad Efron and Trevor Hastie laid out so nicely in their book “Computer Age Statistical Inference: Algorithms, Evidence, and Data Science,” these methods take advantage of today’s increased computing power to solve statistical problems in ways that go far beyond the more standard methods that are usually taught in the undergraduate statistics course for psychology students.

The first year that I taught the class, I used Andy Field’s amazing graphic novel statistics book, “An Adventure in Statistics,” as the textbook. There are many things that I really like about this book – in particular, I like the way that it frames statistical practice around the building of models, and treats null hypothesis testing with sufficient caution. Unfortunately, many of my students disliked the book (except for the English majors, who loved it!), primarily because it involved wading through a lot of story to get to the statistical knowledge. I also found it wanting because there are a number of topics (particularly those from the burgeoning field of artificial intelligence known as *machine learning*) that I wanted to include but were not discussed in his book. I ultimately came to feel that the students would be best served by a book that follows very closely to my lectures, so I started writing down my lectures into a set of computational notebooks that would ultimately become this book. The outline of this book follows roughly that of Field’s book, since the lectures were originally based in large part on the flow of that book, but the content is substantially different (and almost certainly much less fun and clever). I also tailored this book for the 10-week quarter system that we use at Stanford, which provides less time than the 16-week semester that most statistical textbooks are built for.

## 0.2 The golden age of data

Throughout this book I have tried when possible to use examples from real data. This is now very easy because we are swimming in open datasets, as governments, scientists, and companies are increasingly making data freely available. I think that using real datasets is important because it prepares students to work with real data rather than toy datasets, which I think should be one of the major goals of statistical training. It also helps us realize (as we will see at various points throughout the book) that data don’t always come to us ready to analyze, and often need *wrangling* to help get them into shape. Using real data also shows that the idealized statistical distributions often assumed in statistical methods don’t always hold in the real world – for example, as we will see in Chapter 3, distributions of some real-world quantities (like the number of friends on Facebook) can have very long tails that can break many standard assumptions.

I apologize up front that the datasets are heavily US-centric. This is primarily because the best dataset for many of the demonstrations is the National Health and Nutrition Examination Surveys (NHANES) dataset that is available as an R package, and because many of the other complex datasets included in R (such as those in the `fivethirtyeight`

package) are also based in the US. If you have suggestions for datasets from other regions, please pass them along to me!

## 0.3 The importance of doing statistics

The only way to really learn statistics is to *do* statistics. While historically many statistics courses were taught using point-and-click statistical software, it is increasingly common for statistical education to use open-source languages in which students can code their own analyses. I think that being able to code one’s analyses is essential in order to gain a deep appreciation for statistical analysis, which is why the students in my course at Stanford are expected to learn to use the R statistical programming language to analyze data, alongside the theoretical knowledge that they learn from this book.

There are two online companions to this textbook that can help the reader get started learning to program; one focuses on the R programming language, and another focuses on the Python language. Both are currently works in progress – please feel free to contribute!

## 0.4 An open source book

This book is meant to be a living document, which is why its source is available online at https://github.com/statsthinking21/statsthinking21-core. If you find any errors in the book or want to make a suggestion for how to improve it, please open an issue on the Github site. Even better, submit a pull request with your suggested change.

The book is licensed according to the Creative Commons Attribution-NonCommercial 2.0 Generic (CC BY-NC 2.0) License. Please see the terms of that license for more details.

## 0.5 Acknowledgements

I’d first like to thank Susan Holmes, who first inspired me to consider writing my own statistics book. Anna Khazenzon provided early comments and inspiration. Lucy King provided detailed comments and edits on the entire book, and helped clean up the code so that it was consistent with the Tidyverse. Michael Henry Tessler provided very helpful comments on the Bayesian analysis chapter. Particular thanks also go to Yihui Xie, creator of the Bookdown package, for improving the book’s use of Bookdown features (including the ability for users to directly generate edits via the Edit button). Finally, Jeanette Mumford provided very helpful suggestions on the entire book.

I’d also like to thank others who provided helpful comments and suggestions: Athanassios Protopapas, Wesley Tansey, Jack Van Horn, Thor Aspelund.

Thanks to the following Twitter users for helpful suggestions: @enoriverbend

Thanks to the following individuals who have contributed edits or issues by Github or email: Isis Anderson, Larissa Bersh, Isil Bilgin, Forrest Dollins, Chuanji Gao, Nate Guimond, Alan He, Wu Jianxiao, James Kent, Dan Kessler, Philipp Kuhnke, Leila Madeleine, Lee Matos, Ryan McCormick, Jarod Meng, Kirsten Mettler, Shanaathanan Modchalingam, Martijn Stegeman, Mehdi Rahim, Jassary Rico-Herrera, Mingquian Tan, Wenjin Tao, Laura Tobar, Albane Valenzuela, Alexander Wang, Michael Waskom, barbyh, basicv8vc, brettelizabeth, codetrainee, dzonimn, epetsen, carlosivanr, hktang, jiamingkong, khtan, kiyofumi-kan, NevenaK, ttaweel.

Special thanks to Isil Bilgin for assistance in fixing many of these issues.