# Bayesian statistics

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pages: 589 words: 69,193

Mastering Pandas by Femi Anthony

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A Tour of Statistics – The Classical Approach Descriptive statistics versus inferential statistics Measures of central tendency and variability Measures of central tendency The mean The median The mode Computing measures of central tendency of a dataset in Python Measures of variability, dispersion, or spread Range Quartile Deviation and variance Hypothesis testing – the null and alternative hypotheses The null and alternative hypotheses The alpha and p-values Type I and Type II errors Statistical hypothesis tests Background The z-test The t-test Types of t-tests A t-test example Confidence intervals An illustrative example Correlation and linear regression Correlation Linear regression An illustrative example Summary 8. A Brief Tour of Bayesian Statistics Introduction to Bayesian statistics Mathematical framework for Bayesian statistics Bayes theory and odds Applications of Bayesian statistics Probability distributions Fitting a distribution Discrete probability distributions Discrete uniform distributions The Bernoulli distribution The binomial distribution The Poisson distribution The Geometric distribution The negative binomial distribution Continuous probability distributions The continuous uniform distribution The exponential distribution The normal distribution Bayesian statistics versus Frequentist statistics What is probability? How the model is defined Confidence (Frequentist) versus Credible (Bayesian) intervals Conducting Bayesian statistical analysis Monte Carlo estimation of the likelihood function and PyMC Bayesian analysis example – Switchpoint detection References Summary 9.

A Brief Tour of Bayesian Statistics In this chapter, we will take a brief tour of an alternative approach to statistical inference called Bayesian statistics. It is not intended to be a full primer but just serve as an introduction to the Bayesian approach. We will also explore the associated Python-related libraries, how to use pandas, and matplotlib to help with the data analysis. The various topics that will be discussed are as follows: Introduction to Bayesian statistics Mathematical framework for Bayesian statistics Probability distributions Bayesian versus Frequentist statistics Introduction to PyMC and Monte Carlo simulation Illustration of Bayesian inference – Switchpoint detection Introduction to Bayesian statistics The field of Bayesian statistics is built on the work of Reverend Thomas Bayes, an 18th century statistician, philosopher, and Presbyterian minister.

pages: 561 words: 120,899

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JASA (95) 1282–86 Couzin, Jennifer. (2004) The new math of clinical trials. Science (303) 784–86. DeGroot, Morris H. (1986b) A conversation with Persi Diaconis. Statistical Science (1:3) 319–34. Diaconis P, Efron B. (1983) Computer-intensive methods in statistics. Scientific American (248) 116–30. Diaconis, Persi. (1985) Bayesian statistics as honest work. Proceedings of the Berkeley Conference in Honor of Jerzy Neyman and Jack Kiefer (1), eds., Lucien M. Le Cam and Richard A. Olshen. Wadsworth. Diaconis P, Holmes S. (1996) Are there still things to do in Bayesian statistics? Erkenntnis (45) 145–58. Diaconis P. (1998) A place for philosophy? The rise of modeling in statistical science. Quarterly of Applied Mathematics (56:4) 797–805. DuMouchel WH, Harris JE. (1983) Bayes methods for combining the results of cancer studies in humans and other species.

Today, Bayes’ rule is used everywhere from DNA de-coding to Homeland Security. Drawing on primary source material and interviews with statisticians and other scientists, The Theory That Would Not Die is the riveting account of how a seemingly simple theorem ignited one of the greatest controversies of all time”—Provided by publisher. Includes bibliographical references and index. ISBN 978-0-300-16969-0 (hardback) 1. Bayesian statistical decision theory—History. I. Title. QA279.5.M415 2011 519.5’42—dc22 2010045037 A catalogue record for this book is available from the British Library. This paper meets the requirements of ANSI/NISO Z39.48–1992 (Permanence of Paper). 10 9 8 7 6 5 4 3 2 1 When the facts change, I change my opinion. What do you do, sir? —John Maynard Keynes contents Preface and Note to Readers Acknowledgments Part I.

Bayes combined judgments based on prior hunches with probabilities based on repeatable experiments. He introduced the signature features of Bayesian methods: an initial belief modified by objective new information. He could move from observations of the world to abstractions about their probable cause. And he discovered the long-sought grail of probability, what future mathematicians would call the probability of causes, the principle of inverse probability, Bayesian statistics, or simply Bayes’ rule. Given the revered status of his work today, it is also important to recognize what Bayes did not do. He did not produce the modern version of Bayes’ rule. He did not even employ an algebraic equation; he used Newton’s old-fashioned geometric notation to calculate and add areas. Nor did he develop his theorem into a powerful mathematical method. Above all, unlike Price, he did not mention Hume, religion, or God.

pages: 294 words: 81,292

Our Final Invention: Artificial Intelligence and the End of the Human Era by James Barrat

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But by the time the tragedy unfolded, Holtzman told me, Good had retired. He was not in his office but at home, perhaps calculating the probability of God’s existence. According to Dr. Holtzman, sometime before he died, Good updated that probability from zero to point one. He did this because as a statistician, he was a long-term Bayesian. Named for the eighteenth-century mathematician and minister Thomas Bayes, Bayesian statistics’ main idea is that in calculating the probability of some statement, you can start with a personal belief. Then you update that belief as new evidence comes in that supports your statement or doesn’t. If Good’s original disbelief in God had remained 100 percent, no amount of data, not even God’s appearance, could change his mind. So, to be consistent with his Bayesian perspective, Good assigned a small positive probability to the existence of God to make sure he could learn from new data, if it arose.

pages: 397 words: 102,910

The Idealist: Aaron Swartz and the Rise of Free Culture on the Internet by Justin Peters

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So we need an algorithm or computer program that would encourage lots of people to identify the fights and to start the campaigns,” McLean told the Sydney Morning Herald in 2014. “We’d put the tools that we have at our disposal in their hands.”32 Swartz had actually been building tools like these for several months with his colleagues at ThoughtWorks. Victory Kit, as the project was called, was an open-source version of the expensive community-organizing software used by groups such as MoveOn. Victory Kit incorporated Bayesian statistics—an analytical method that gets smarter as it goes along by consistently incorporating new information into its estimates—to improve activists’ ability to reach and organize their bases. “In the end, a lot of what the software was about was doing quite sophisticated A/B testing of messages for advocacy,” remembered Swartz’s friend Nathan Woodhull.33 Swartz was scheduled to present Victory Kit to the group at the Holmes retreat.

Ashcroft, 137–38, 140 FBI file on, 191–92, 223 fleeing the system, 8, 145, 151, 158–59, 161, 171, 173, 193, 248, 267 and free culture movement, 3–4, 141, 152–55, 167, 223 and Harvard, 3, 205, 207, 223, 224, 229 health issues of, 9, 150, 165–66, 222 immaturity of, 8–9 and Infogami, 147, 148–51, 158 interests of, 6–7, 8–9, 204, 221 “Internet and Mass Collaboration, The,” 166–67 lawyers for, 6, 254–55 legacy of, 14–15, 268, 269–70 and Library of Congress, 139 and Malamud, 187–93, 222, 223 manifesto of, 6–7, 178–81, 189–90, 201, 228–30, 247 mass downloading of documents by, 1, 3, 188–94, 197–202, 207, 213, 215, 222, 228, 235 media stories about, 125 and MIT, 1, 3, 201, 204, 207, 213, 222, 227, 232, 249–50, 262 and money, 170–71 on morality and ethics, 205–6 and Open Library, 163, 173, 179, 223, 228 and PCCC, 202–3, 225 as private person/isolation of, 2–3, 5, 124, 127, 143, 154–55, 158–60, 166, 169, 205, 224, 227, 228, 248–49, 251 and public domain, 123 as public speaker, 213–14, 224, 243, 257 and Reddit, see Reddit The Rules broken by, 14 “saving the world” on bucket list of, 7, 8, 15, 125, 151–52, 181, 205–6, 247–48, 266, 267, 268 self-help program of, 251–53 and theinfo.org, 172–73 and US Congress, 224–25, 239–40 Swartz, Robert: and Aaron’s death, 261, 262, 264 and Aaron’s early years, 124, 127 and Aaron’s legal woes, 232, 250, 254 and MIT Media Lab, 203–4, 212, 219, 232, 250 and technology, 124, 212 Swartz, Susan, 128–29, 160, 192 Swartz’s legal case: as “the bad thing,” 3, 7–8, 234 change in defense strategy, 256–57 evidence-suppression hearing, 259–60 facts of, 11 felony charges in, 235, 253 grand jury, 232–33 indictment, 1, 5, 8, 10, 11, 233, 234, 235–37, 241, 253–54 investigation and capture, 215–17, 223, 228 JSTOR’s waning interest in, 231–32 manifesto as evidence in, 228–30 motion to suppress, 6 motives sought in, 223, 229 Norton subpoenaed in, 1–2, 227–29 ongoing, 248, 249–51 online petitions against, 236–37 original charges in, 218, 222 plea deals offered, 227, 250 possible prison sentence, 1, 2, 5, 7–8, 11, 222, 232, 235–36, 253, 260 potential harm assessed, 218, 219, 222, 235 prosecutor’s zeal in, 7–8, 11, 218, 222–24, 235–37, 253–54, 259–60, 263, 264 search and seizure in, 6, 223–24, 256–57 Symbolics, 103 systems, flawed, 265–67 T. & J. W. Johnson, 49 Tammany Hall, New York, 57 tech bubble, 146, 156 technology: Bayesian statistics in, 258–59 burgeoning, 69, 71, 84, 87–88 communication, 12, 13, 18, 87–88 computing, see computers and digital culture, 122 and digital utopia, 91, 266–67 of electronic publishing, 120 and intellectual property, 90–91 and irrational exuberance, 146 in library of the future, 81–83 as magic, 152 moving inexorably forward, 134 overreaching police action against, 233 power of metadata, 128, 130 as private property, 210 resisting change caused by, 120 saving humanity via, 101 thinking machines, 102 unknown, future, 85 and World War II, 208 telephone, invention of, 69 Templeton, Brad, 261 theinfo.org, 172–73 theme parks, 134 ThoughtWorks, 9, 248, 257, 258 “thumb drive corps,” 187, 191, 193 Toyota Motor Corporation, “lean production” of, 7, 257, 265 Trumbull, John, McFingal, 26 trust-busting, 75 Tucher, Andie, 34 Tufte, Edward, 263–64 “tuft-hunter,” use of term, 28 Tumblr, 240 Twain, Mark, 60, 62, 73 Tweed, William “Boss,” 57 Twitter, 237 Ulrich, Lars, 133 United States: Articles of Confederation, 26 copyright laws in, 26–27 economy of, 44–45, 51, 55, 56 freedom to choose in, 80, 269 industrialization, 57 literacy in, 25, 26–27, 39, 44, 48 migration to cities in, 57 national identity of, 28, 32 new social class in, 69–70 opportunity in, 58, 80 poverty in, 59 railroads, 55, 56 rustic nation of, 44–45 values of, 85 UNIVAC computer, 81, 90 Universal Studios Orlando, 134 University of Illinois at Urbana-Champaign, 94, 95–96, 112–15 Unix, 104 US Chamber of Commerce, 239 utilitarianism, 214 Valenti, Jack, 111, 132 Van Buren, Martin, 44 Van Dyke, Henry, The National Sin of Literary Piracy, 61 venture capital, 146 Viaweb, 146 Victor, O.

pages: 319 words: 90,965

The End of College: Creating the Future of Learning and the University of Everywhere by Kevin Carey

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In describing how the brain reacts to surprise, Lue said that “everything is a function of risk and opportunity.” To survive and prosper in the world with limited cognitive capacity, humans filter waves of constant sensory information through neural patterns—heuristics and mental shortcuts that our minds use to weigh the odds that what we are sensing is familiar and categorizable based on our past experience. Sebastian Thrun’s self-driving car does this with Bayesian statistics built into silicon and code, while the human mind uses electrochemical processes that we still don’t fully understand. But the underlying principle is the same: Based on the pattern of lines and shapes and edges, that is probably a boulder and I should drive around it. That is probably a group of three young women eating lunch at a table near the sushi bar and I should pay them no mind. Heuristics are also critically important to the market for higher education.

., 90–91, 98 Air Force, 91 Artificial Intelligence (AI), 11, 79, 136, 153, 159, 170, 264n Adaptive Control of Thought—Rational (ACT-R) model for, 101–4 cognitive tutoring using, 103, 105, 138, 179, 210 Dartmouth conference on, 79, 101 learning pathways for, 155 personalized learning with, 5, 232 theorem prover based in, 110 Thrun’s work in, 147–50 Arum, Richard, 9, 10, 36, 85, 244 Associate’s degrees, 6, 61, 117, 141, 193, 196, 198 Atlantic magazine, 29, 65, 79, 123 AT&T, 146 Australian National University, 204 Bachelor’s degrees, 6–9, 31, 36, 60–61, 64 for graduate school admission, 30 percentage of Americans with, 8, 9, 57, 77 professional versus liberal arts, 35 required for public school teachers, 117 social mobility and, 76 time requirement for, 6, 22 value in labor market of, 58 Badges, digital, 207–12, 216–18, 233, 245, 248 Barzun, Jacques, 32–34, 44, 45, 85 Bayesian statistics, 181 Bell Labs, 123–24 Bellow, Saul, 59, 78 Berlin, University of, 26, 45-46 Bhave, Amol, 214–15 Bing, 212 Binghamton, State University of New York at, 183–84 Bishay, Shereef, 139, 140 Bloomberg, Michael, 251 Blue Ocean Strategy (Kim and Mauborgne), 130 Bologna, University of, 16–17, 21, 41 Bonn, University of, 147 Bonus Army, 51 Borders Books, 127 Boston College, 164, 175 Boston Gazette, 95 Boston Globe, 2 Boston University (BU), 59, 61–62, 64 Bowen, William G., 112–13 Bowman, John Gabbert, 74–75 Brigham Young University, 2 Brilliant, 213 British Army, 98 Brookings Institution, 54 Brooklyn College, 44 Brown v.

pages: 829 words: 186,976

The Signal and the Noise: Why So Many Predictions Fail-But Some Don't by Nate Silver

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Scott Armstrong, The Wharton School, University of Pennsylvania LIBRARY OF CONGRESS CATALOGING IN PUBLICATION DATA Silver, Nate. The signal and the noise : why most predictions fail but some don’t / Nate Silver. p. cm. Includes bibliographical references and index. ISBN 978-1-101-59595-4 1. Forecasting. 2. Forecasting—Methodology. 3. Forecasting—History. 4. Bayesian statistical decision theory. 5. Knowledge, Theory of. I. Title. CB158.S54 2012 519.5'42—dc23 2012027308 While the author has made every effort to provide accurate telephone numbers, Internet addresses, and other contact information at the time of publication, neither the publisher nor the author assumes any responsibility for errors, or for changes that occur after publication. Further, publisher does not have any control over and does not assume any responsibility for author or third-party Web sites or their content.

In essence, this player could go to work every day for a year and still lose money. This is why it is sometimes said that poker is a hard way to make an easy living. Of course, if this player really did have some way to know that he was a long-term winner, he’d have reason to persevere through his losses. In reality, there’s no sure way for him to know that. The proper way for the player to estimate his odds of being a winner, instead, is to apply Bayesian statistics,31 where he revises his belief about how good he really is, on the basis of both his results and his prior expectations. If the player is being honest with himself, he should take quite a skeptical attitude toward his own success, even if he is winning at first. The player’s prior belief should be informed by the fact that the average poker player by definition loses money, since the house takes some money out of the game in the form of the rake while the rest is passed around between the players.32 The Bayesian method described in the book The Mathematics of Poker, for instance, would suggest that a player who had made \$30,000 in his first 10,000 hands at a \$100/\$200 limit hold ’em game was nevertheless more likely than not to be a long-term loser.

McGrayne, The Theory That Would Not Die, Kindle location 7. 61. Raymond S. Nickerson, “Null Hypothesis Significance Testing: A Review of an Old and Continuing Controversy,” Psychological Methods, 5, 2 (2000), pp. 241–301. http://203.64.159.11/richman/plogxx/gallery/17/%E9%AB%98%E7%B5%B1%E5%A0%B1%E5%91%8A.pdf. 62. Andrew Gelman and Cosma Tohilla Shalizi, “Philosophy and the Practice of Bayesian Statistics,” British Journal of Mathematical and Statistical Psychology, pp. 1–31, January 11, 2012. http://www.stat.columbia.edu/~gelman/research/published/philosophy.pdf. 63. Although there are several different formulations of the steps in the scientific method, this version is mostly drawn from “APPENDIX E: Introduction to the Scientific Method,” University of Rochester. http://teacher.pas.rochester.edu/phy_labs/appendixe/appendixe.html. 64.

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The Moral Landscape: How Science Can Determine Human Values by Sam Harris

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If we are measuring sanity in terms of sheer numbers of subscribers, then atheists and agnostics in the United States must be delusional: a diagnosis which would impugn 93 percent of the members of the National Academy of Sciences.63 There are, in fact, more people in the United States who cannot read than who doubt the existence of Yahweh.64 In twenty-first-century America, disbelief in the God of Abraham is about as fringe a phenomenon as can be named. But so is a commitment to the basic principles of scientific thinking—not to mention a detailed understanding of genetics, special relativity, or Bayesian statistics. The boundary between mental illness and respectable religious belief can be difficult to discern. This was made especially vivid in a recent court case involving a small group of very committed Christians accused of murdering an eighteen-month-old infant.65 The trouble began when the boy ceased to say “Amen” before meals. Believing that he had developed “a spirit of rebellion,” the group, which included the boy’s mother, deprived him of food and water until he died.

The ACC and the caudate display an unusual degree of connectivity, as the surgical lesioning of the ACC (a procedure known as a cingulotomy) causes atrophy of the caudate, and the disruption of this pathway is thought to be the basis of the procedure’s effect in treating conditions like obsessive-compulsive disorder (Rauch et al., 2000; Rauch et al., 2001). There are, however, different types of uncertainty. For instance, there is a difference between expected uncertainty—where one knows that one’s observations are unreliable—and unexpected uncertainty, where something in the environment indicates that things are not as they seem. The difference between these two modes of cognition has been analyzed within a Bayesian statistical framework in terms of their underlying neurophysiology. It appears that expected uncertainty is largely mediated by acetylcholine and unexpected uncertainty by norepinephrine (Yu & Dayan, 2005). Behavioral economists sometimes distinguish between “risk” and “ambiguity”: the former being a condition where probability can be assessed, as in a game of roulette, the latter being the uncertainty borne of missing information.

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The Master Algorithm: How the Quest for the Ultimate Learning Machine Will Remake Our World by Pedro Domingos

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The distinction between descriptive and normative theories was articulated by John Neville Keynes in The Scope and Method of Political Economy (Macmillan, 1891). Chapter Six Sharon Bertsch McGrayne tells the history of Bayesianism, from Bayes and Laplace to the present, in The Theory That Would Not Die (Yale University Press, 2011). A First Course in Bayesian Statistical Methods,* by Peter Hoff (Springer, 2009), is an introduction to Bayesian statistics. The Naïve Bayes algorithm is first mentioned in Pattern Classification and Scene Analysis,* by Richard Duda and Peter Hart (Wiley, 1973). Milton Friedman argues for oversimplified theories in “The methodology of positive economics,” which appears in Essays in Positive Economics (University of Chicago Press, 1966). The use of Naïve Bayes in spam filtering is described in “Stopping spam,” by Joshua Goodman, David Heckerman, and Robert Rounthwaite (Scientific American, 2005).

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The Rise of the Quants: Marschak, Sharpe, Black, Scholes and Merton by Colin Read

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He postulated that the rational decision-maker will align his or her beliefs of unknown probabilities to the consensus bets of impartial bookmakers, a technique often called the Dutch Book. Thirty later, the great mind Leonard “Jimmie” Savage (1917–1971) elaborated his concept into an axiomatic approach to decision-making under uncertainty using arguments remarkably similar to Ramsey’s logic. The concepts of Ramsey and Savage also formed the basis for the theory of Bayesian statistics and are important in many aspects of financial decision-making. Marschak’s great insight While Ramsey created and Savage broadened the logical landscape for the inclusion of uncertainty into decision-making, it was not possible to incorporate their logic until the finance discipline could develop actual measures of uncertainty. Of course, modern financial analysis depends crucially even today on such a methodology to measure uncertainty.

pages: 654 words: 191,864

Thinking, Fast and Slow by Daniel Kahneman

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So if you believe that there is a 40% chance plethat it will rain sometime tomorrow, you must also believe that there is a 60% chance it will not rain tomorrow, and you must not believe that there is a 50% chance that it will rain tomorrow morning. And if you believe that there is a 30% chance that candidate X will be elected president, and an 80% chance that he will be reelected if he wins the first time, then you must believe that the chances that he will be elected twice in a row are 24%. The relevant “rules” for cases such as the Tom W problem are provided by Bayesian statistics. This influential modern approach to statistics is named after an English minister of the eighteenth century, the Reverend Thomas Bayes, who is credited with the first major contribution to a large problem: the logic of how people should change their mind in the light of evidence. Bayes’s rule specifies how prior beliefs (in the examples of this chapter, base rates) should be combined with the diagnosticity of the evidence, the degree to which it favors the hypothesis over the alternative.

Analysis of Financial Time Series by Ruey S. Tsay

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In this chapter, we introduce the ideas of MCMC methods and data augmentation that are widely applicable in finance. In particular, we discuss Bayesian inference via Gibbs sampling and demonstrate various applications of MCMC methods. Rapid developments in the MCMC methodology make it impossible to cover all the new methods available in the literature. Interested readers are referred to some recent books on Bayesian and empirical Bayesian statistics (e.g., Carlin and Louis, 2000; Gelman, Carlin, Stern, and Rubin, 1995). For applications, we focus on issues related to financial econometrics. The demonstrations shown in this chapter only represent a small fraction of all possible applications of the techniques in finance. As a matter of fact, it is fair to say that Bayesian inference and the MCMC methods discussed here are applicable to most, if not all, of the studies in financial econometrics.

Such a prior distribution is called a conjugate prior distribution. For MCMC methods, use of conjugate priors means that a closed-form solution for the conditional posterior distributions is available. Random draws of the Gibbs sampler can then be obtained by using the commonly available computer routines of probability distributions. In what follows, we review some well-known conjugate priors. For more information, readers are referred to textbooks on Bayesian statistics (e.g., DeGroot, 1970, Chapter 9). Result 1: Suppose that x1 , . . . , xn form a random sample from a normal distribution with mean µ, which is unknown, and variance σ 2 , which is known and positive. Suppose that the prior distribution of µ is a normal distribution with mean µo and variance σo2 . Then the posterior distribution of µ given the data and prior is 401 BAYESIAN INFERENCE normal with mean µ∗ and variance σ∗2 given by µ∗ = σ 2 µo + nσo2 x̄ σ 2 + nσo2 and σ∗2 = σ 2 σo2 , σ 2 + nσo2 n xi /n is the sample mean. where x̄ = i=1 In Bayesian analysis, it is often convenient to use the precision parameter η = 1/σ 2 (i.e., the inverse of the variance σ 2 ).

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Data Scientists at Work by Sebastian Gutierrez

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The Data Revolution: Big Data, Open Data, Data Infrastructures and Their Consequences by Rob Kitchin

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Inferential statistics seek to explain, not simply describe, the patterns and relationships that may exist within a dataset, and to test the strength and significance of associations between variables. They include parametric statistics which are employed to assess hypotheses using interval and ratio level data, such as correlation and regression; non-parametric statistics used for testing hypotheses using nominal or ordinal-level data; and probabilistic statistics that determine the probability of a condition occurring, such as Bayesian statistics. The armoury of descriptive and inferential statistics that have traditionally been used to analyse small data are also being applied to big data, though as discussed in Chapter 9 this is not always straightforward because many of these techniques were developed to draw insights from relatively scarce rather than exhaustive data. Nonetheless, the techniques do provide a means of making sense of massive amounts of data.

pages: 398 words: 120,801

Little Brother by Cory Doctorow

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They hopped from Xbox to Xbox until they found one that was connected to the Internet, then they injected their material as undecipherable, encrypted data. No one could tell which of the Internet's packets were Xnet and which ones were just plain old banking and e-commerce and other encrypted communication. You couldn't find out who was tying the Xnet, let alone who was using the Xnet. But what about Dad's "Bayesian statistics?" I'd played with Bayesian math before. Darryl and I once tried to write our own better spam filter and when you filter spam, you need Bayesian math. Thomas Bayes was an 18th century British mathematician that no one cared about until a couple hundred years after he died, when computer scientists realized that his technique for statistically analyzing mountains of data would be super-useful for the modern world's info-Himalayas.

pages: 755 words: 121,290

Statistics hacks by Bruce Frey

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William Skorupski is currently an assistant professor in the School of Education at the University of Kansas, where he teaches courses in psychometrics and statistics. He earned his Bachelor's degree in educational research and psychology from Bucknell University in 2000, and his Doctorate in psychometric methods from the University of Massachusetts, Amherst in 2004. His primary research interest is in the application of mathematical models to psychometric data, including the use of Bayesian statistics for solving practical measurement problems. He also enjoys applying his knowledge of statistics and probability to everyday situations, such as playing poker against the author of this book! Acknowledgments I'd like to thank all the contributors to this book, both those who are listed in the "Contributors" section and those who helped with ideas, reviewed the manuscript, and provided suggestions of sources and resources.

pages: 483 words: 141,836

Red-Blooded Risk: The Secret History of Wall Street by Aaron Brown, Eric Kim

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If you accept that your entire earthly life is the appropriate numeraire for decision making, then the rest of Pascal’s case is easy to accept. Just as Archimedes claimed that with a long enough lever he could move the earth, I claim that with a big enough numeraire, I can make any faith-based action seem reasonable. Frequentist statistics suffers from paradoxes because it doesn’t insist everything be stated in moneylike terms, without which there’s no logical connection between frequency and degree of belief. Bayesian statistics suffers from insisting on a single, universal numeraire, which is often not appropriate. One thing we know about money is that it can’t buy everything. One thing we know about people is they have multiple natures, and groups of people are even more complicated. There are many numeraires, more than there are people. Picking the right one is key to getting meaningful statistical results. The only statistical analyses that can be completely certain are ones that are pure mathematical results, and ones that refer to gamelike situations in which all outside considerations are excluded by rule and the numeraire is specified.

pages: 574 words: 164,509

Superintelligence: Paths, Dangers, Strategies by Nick Bostrom

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They also provide important insight into the concept of causality.28 One advantage of relating learning problems from specific domains to the general problem of Bayesian inference is that new algorithms that make Bayesian inference more efficient will then yield immediate improvements across many different areas. Advances in Monte Carlo approximation techniques, for example, are directly applied in computer vision, robotics, and computational genetics. Another advantage is that it lets researchers from different disciplines more easily pool their findings. Graphical models and Bayesian statistics have become a shared focus of research in many fields, including machine learning, statistical physics, bioinformatics, combinatorial optimization, and communication theory.35 A fair amount of the recent progress in machine learning has resulted from incorporating formal results originally derived in other academic fields. (Machine learning applications have also benefitted enormously from faster computers and greater availability of large data sets

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Against the Gods: The Remarkable Story of Risk by Peter L. Bernstein

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Jahn Maynard Keynes. Vol. 1: Hopes Betrayed. New York: Viking. Slovic, Paul, Baruch Fischoff, and Sarah Lichtenstein, 1990. "Rating the Risks." In Glickman and Gough, 1990, pp. 61-75. Smith, Clifford W., Jr., 1995. "Corporate Risk Management: Theory and Practice." Journal of Derivatives, Summer, pp. 21-30. Smith, M. F. M., 1984. "Present Position and Potential Developments: Some Personal Views of Bayesian Statistics." Journal of the Royal Statistical Association, Vol. 147, Part 3, pp. 245-259. Smithson, Charles W., and Clifford W. Smith, Jr., 1995. Managing Financial Risk: A Guide to Derivative Products, Financial Engineering, and Value Maximization. New York: Irwin.* Sorensen, Eric, 1995. "The Derivative Portfolio Matrix-Combining Market Direction with Market Volatility." Institute for Quantitative Research in Finance, Spring 1995 Seminar.

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Algorithms to Live By: The Computer Science of Human Decisions by Brian Christian, Tom Griffiths

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Laplace was born in Normandy: For more details on Laplace’s life and work, see Gillispie, Pierre-Simon Laplace. distilled down to a single estimate: Laplace’s Law is derived by working through the calculation suggested by Bayes—the tricky part is the sum over all hypotheses, which involves a fun application of integration by parts. You can see a full derivation of Laplace’s Law in Griffiths, Kemp, and Tenenbaum, “Bayesian Models of Cognition.” From the perspective of modern Bayesian statistics, Laplace’s Law is the posterior mean of the binomial rate using a uniform prior. If you try only once and it works out: You may recall that in our discussion of multi-armed bandits and the explore/exploit dilemma in chapter 2, we also touched on estimates of the success rate of a process—a slot machine—based on a set of experiences. The work of Bayes and Laplace undergirds many of the algorithms we discussed in that chapter, including the Gittins index.

pages: 685 words: 203,949

The Organized Mind: Thinking Straight in the Age of Information Overload by Daniel J. Levitin

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For every 5 people who take the treatment, 1 will be cured (because that person actually has the disease) and .25 will have the side effects. In this case, with two tests, you’re now about 4 times more likely to experience the cure than the side effects, a nice reversal of what we saw before. (If it makes you uncomfortable to talk about .25 of a person, just multiply all the numbers above by 4.) We can take Bayesian statistics a step further. Suppose a newly published study shows that if you are a woman, you’re ten times more likely to get the disease than if you’re a man. You can construct a new table to take this information into account, and to refine the estimate that you actually have the disease. The calculations of probabilities in real life have applications far beyond medical matters. I asked Steve Wynn, who owns five casinos (at his Wynn and Encore hotels in Las Vegas, and the Wynn, Encore, and Palace in Macau), “Doesn’t it hurt, just a little, to see customers walking away with large pots of your money?”

pages: 827 words: 239,762

The Golden Passport: Harvard Business School, the Limits of Capitalism, and the Moral Failure of the MBA Elite by Duff McDonald

Anyone who has come across a decision tree when contemplating the choices and uncertainties in business owes them a debt. In short, their work opened up just about any business problem to mathematical analysis, without necessarily sacrificing expert opinion in the process. In 1959, Schlaifer published Probability and Statistics for Business Decisions, and in 1961, Raiffa and Schlaifer coauthored Applied Statistical Decision Theory, which “set the direction of Bayesian statistics for the next two decades.”10 But this was geeky stuff, especially for the more “broad-gauged” crowd at HBS. So even if the School was trying as hard as it could to keep up with the GSIAs of the world, it still felt a need to apologize for getting too geeky with Applied Statistical Decision Theory. Calling it “a new type of publication,” Dean Teele explained that “[whereas] most reports . . . published by the Division of Research have as their intended audience informed and forward-looking business executives in general, the new series has been written primarily for specialists. . . .”11 Translation: You may not understand it, but that doesn’t mean you’re not “informed and forward-looking.”

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Rationality: From AI to Zombies by Eliezer Yudkowsky

Some frequentists criticize Bayesians for treating probabilities as subjective states of belief, rather than as objective frequencies of events. Kruschke and Yudkowsky have replied that frequentism is even more “subjective” than Bayesianism, because frequentism’s probability assignments depend on the intentions of the experimenter.10 Importantly, this philosophical disagreement shouldn’t be conflated with the distinction between Bayesian and frequentist data analysis methods, which can both be useful when employed correctly. Bayesian statistical tools have become cheaper to use since the 1980s, and their informativeness, intuitiveness, and generality have come to be more widely appreciated, resulting in “Bayesian revolutions” in many sciences. However, traditional frequentist methods remain more popular, and in some contexts they are still clearly superior to Bayesian approaches. Kruschke’s Doing Bayesian Data Analysis is a fun and accessible introduction to the topic.11 In light of evidence that training in statistics—and some other fields, such as psychology—improves reasoning skills outside the classroom, statistical literacy is directly relevant to the project of overcoming bias.

I responded—note that this was completely spontaneous—“What on Earth do you mean? You can’t avoid assigning a probability to the mathematician making one statement or another. You’re just assuming the probability is 1, and that’s unjustified.” To which the one replied, “Yes, that’s what the Bayesians say. But frequentists don’t believe that.” And I said, astounded: “How can there possibly be such a thing as non-Bayesian statistics?” That was when I discovered that I was of the type called “Bayesian.” As far as I can tell, I was born that way. My mathematical intuitions were such that everything Bayesians said seemed perfectly straightforward and simple, the obvious way I would do it myself; whereas the things frequentists said sounded like the elaborate, warped, mad blasphemy of dreaming Cthulhu. I didn’t choose to become a Bayesian any more than fishes choose to breathe water.