The Art of Data Analysis

How to Answer Almost Any Question Using Basic Statistics

Kristin H. Jarman

• Publisher: Wiley
• Year: 2013
• ISBN:
  9781118413340
• Edition: 1
• Topic: Matematica
• Subtopic: Probabilità e statistica

A friendly and accessible approach to applying statistics in the real world With an emphasis on critical thinking, The Art of Data Analysis: How to Answer Almost Any Question Using Basic Statistics presents fun and unique examples, guides readers through the entire data collection and analysis process, and introduces basic statistical concepts along the way. Leaving proofs and complicated mathematics behind, the author portrays the more engaging side of statistics and emphasizes its role as a problem-solving tool. In addition, light-hearted case studies illustrate the application of statistics to real data analyses, highlighting the strengths and weaknesses of commonly used techniques. Written for the growing academic and industrial population that uses statistics in everyday life, The Art of Data Analysis: How to Answer Almost Any Question Using Basic Statistics highlights important issues that often arise when collecting and sifting through data. Featured concepts include:

• Descriptive statistics
• Analysis of variance
• Probability and sample distributions
• Confidence intervals
• Hypothesis tests
• Regression
• Statistical correlation
• Data collection
• Statistical analysis with graphs

Fun and inviting from beginning to end, The Art of Data Analysis is an ideal book for students as well as managers and researchers in industry, medicine, or government who face statistical questions and are in need of an intuitive understanding of basic statistical reasoning.

Part 1

The Basics

Chapter 1

Statistics: The Life of the Party

As I sat in my favorite coffee shop, latte in hand, wondering how to introduce this book, my mind drifted to the conversations around me. At the table to my right sat a couple of college guys, decked out in sweatshirts touting a nearby university. They were arguing baseball, speculating which team was most likely to win the pennant and make it to the World Series. To my left sat three middle-aged women, speaking in quiet voices I had to strain to hear. They were talking about menopause, comparing their own experiences, trying to sort through the conflicting news about which, if any, treatments actually alleviate the symptoms. Behind me was the liveliest conversation of all. Two men were talking politics. Both men seemed to agree about who should win the next presidential election, but that didn’t keep them from arguing. Many words were exchanged, but it came down to this. One of the men, citing a national poll, insisted his candidate was clearly going to be the winner. The other, citing yet another poll, claimed the outcome was anybody’s guess.

Aside from my tendency to eavesdrop, there’s a common theme to the three conversations. Whether they knew it or not, all of these people were talking statistics.

Most people run across statistics on a daily basis. In fact, in this age of instant information, it’s hard to get away from them. Drug studies, stock market projections, sales trends, sports, education, crime reports: the list of places you’ll find them goes on and on. Any time somebody takes a large amount of information and reduces it down to a few bullet points, that person is using statistics. And even if you never look at any raw data, when you use those bullet points to make conclusions or decisions, you’re using statistics as well.

Being a statistician has never made me the life of the party. In fact, when I meet a new person, the reaction to my profession is almost universal. Here’s how a typical conversation might go.

Me:	How do you know John?
New Friend:	We work together at XYZ Corp. I’m in sales, and John’s in marketing. How about you?
Me:	Oh, we’ve worked together on a few projects as well. So, are you married?
New Friend:	Yeah, sure. What projects?
Me:	The Michelson account, the Trends Survey, a few others. How ‘bout kids? Do you have kids?
New Friend:	Hey, I worked on the Michelson account, too. Ran the sales campaign. But I don’t remember you.
Me (glancing around the room):	I was just a consultant.
New Friend:	Hey, wait a minute. I do remember you. You told us we couldn’t launch the product in June . . . something about summer and . . .
Me (shrugging):	Seasonal effects on customer demand. Yes, that’s me. I’m the statistician.
(There’s a long, awkward pause. New Friend eyes me suspiciously.)
New Friend:	I always hated statistics.

It may not be the life of the party, but when it comes to sorting through mounds of information, statistics is the belle of the ball. And it doesn’t take a graduate degree in the subject to know how to use it. If you can apply a few basic statistical tools and a little practical knowledge to a problem, people think you’re genius, and maybe even a little clairvoyant. These qualities may not draw crowds at the neighborhood mixer, but they do tend to result in big raises and big promotions.

Real-world statistics isn’t only about calculating an average and a standard deviation. And it’s not always a highly precise, exact science. Statistics involves gathering data and distilling large amounts of information down to a reasonable and accurate conclusion. Most statistical analyses begin not with a dataset, but with a question. What will be the impact of our new marketing campaign? Does this drug work? Who’s most likely to win the next presidential election? Answering these questions takes more than a spreadsheet and a few formulas. It’s a process: reducing the question down to a manageable size, collecting data, understanding what the data are telling you, and yes, eventually making some calculations. Often this process is as much an art as it is a science. And it is this art, the art of data analysis, that provides you with the tools you need to understand your data.

There are no proofs in pages that follow. Mathematical formulas are kept to a bare minimum. Instead, this book deals with the practical and very real-world problem of data analysis. Each chapter asks a question and illustrates how it might be answered using techniques taught in any introductory statistics course. Along the way, common issues come up, issues such as:

• How to turn a vaguely worded question into a scientific study
• How different types of statistical analyses are well-suited to different types of questions
• How a well-chosen plot can do most of the data analysis for you
• How to identify the limitations of a study
• What happens if your data aren’t perfect
• How to avoid misleading or completely false conclusions

Every chapter is a case study, complete with a question, a data collection effort, and a statistical analysis. None of these case studies addresses society’s fundamental problems (unless you think the lack of appreciation for superhero sidekicks is one of them). None of them will help you improve your company’s sales (unless those sales are dependent on scientific proof that Bigfoot exists). And none of them will help you pick up women (especially not the one about gender stereotypes). On the other hand, all of them can be used as a template for your own data analysis, whether it be for a classroom project, a work-related problem, or a personal bet you just must win. And all of them illustrate how basic data analysis can be used to answer almost any question you can imagine.

The statistical techniques presented here can be found in most spreadsheet programs and basic data analysis software. I used Microsoft Excel throughout, and in some cases, the Analysis Add-In pack was required. Here and there, a specific function is mentioned, but this isn’t a book on statistics using Excel. There are plenty of good texts covering that topic. Some of the most popular, written by a man known as Mr. Spreadsheet, are listed in the Bibliography at the end of this chapter.

The outline of this book follows a typical introductory statistics course. Part One gives you the basic tools you need to ask a question and design a study to answer it. Part Two shows what you can do with a solid understanding of these basic tools. Each chapter is self-contained, but like a typical textbook, the concepts build on one another, and the analyses gradually become more sophisticated as the book progresses. If you’re dying of curiosity and you’ve just got to find out when the zombie flu went viral, then go ahead and jump to Chapter 9. But if you can wait, I recommend you turn the page and read through the chapters in order.

I hope you enjoy reading these case studies as much as I enjoyed writing them.

Bibliography

Walkenbach, John. 2007. Excel 2007 Charts. Wiley.

Walkenbach, John. 2010. Excel 2010 Bible. Wiley.

Walkenbach, John. 2010. Excel 2010 Formulas. Wiley.

Walkenbach, John. 2010. John Walkenbach’s Favorite Excel 2010 Tips and Tricks. Wiley.

Chapter 2

Lions, and Tigers, and . . . Bigfoot? Oh, My: How Questionable Data Can Screw Up an Otherwise Perfectly Good Statistical Analysis

The mountain devil. Jacko. Sasquatch. Bigfoot. These are just a few names for a mysterious apelike creature rumored to be living in mountain forests around the United States. He’s been a legend for generations. Ancient stone carvings of humanlike ape heads have been excavated in the Pacific Northwest (Eberhart 2001). Newspaper articles from the 1800s report “wild men” in such diverse geographic areas as Pennsylvania and California (Bord and Bord 2006). In the early 1900s, settlers and prospectors frequently reported seeing this creature in California, Washington, and Oregon (Bord and Bord 2006). There have been thousands of reported Bigfoot sightings in the last hundred years alone. And yet, no solid scientific proof of the creature exists.

Some of the eyewitnesses are con artists, to be sure. In 2008, for example, two gentlemen in Georgia threw slaughterhouse leftovers and a gorilla suit into a meat freezer, filmed the scene, and posted the video on YouTube, claiming they’d found the discovery of the century. The hoax only lasted a few days. Worldwide scrutiny soon got to the men, and they admitted it was all just a prank (CNN 2008).

Other sightings cannot be dismissed so easily. They come from seemingly reliable and trustworthy people, such as hunters, outdoorsmen, and soldiers, quiet residents who inhabit the very forests Bigfoot is reported to inhabit. Their reports are so vivid and so consistent, Bigfoot researchers have even compiled a detailed description of the creature, right down to the sounds he makes and his social behavior (Eberhart 2001).

The evidence doesn’t end with eyewitness reports. Footprints, too large and square to be human, have been discovered, photographed, cast in plaster, and studied in detail. Hair samples of questionable origin have been collected. There’s even a controversial film, shot in 1967 by Roger Patterson and Bob Gimlin. In this film, a large ape-man (or ape-woman, as some experts believe) walks through the forests of northern California. She’s even so obliging as to glance at the camera while she passes.

With all this so-called evidence, Bigfoot researchers should have no trouble proving the existence of the creature. But this proof remains as elusive as the creature himself. Controversy over the Patterson film’s authenticity rages on. DNA analysis of hair samples has, to date, been inconclusive. And even the best footprints somehow manage to look more fake than real. The most skeptical among us believe Bigfoot is pure myth, the subject of campfire stories and other tall tales. Others think the creature was real, a North American ape, perhaps, that once lived among early humans but long ago became extinct. Still others think the creature is alive and well, extremely shy, and living in remote areas across the United States.

Let’s say, for argument’s sake, I’m one of the believers. I’m convinced Bigfoot’s real. Let’s say, hypothetically speaking, I’m excited about the idea, so excited I just have to do something about it. I quit my job and head off in search of the creature. With visions of fame and fortune running through my head, I cash in my savings, say goodbye to my family, and drive away in my newly purchased vintage mini-bus.

As I leave the city limits, my thoughts turn to the task ahead. Bigfoot exists, there’s no doubt about it. He’s out there, waiting to be discovered. And who better than a statistician-turned-monster-hunter to discover him? I’ve got scientific objectivity, some newly acquired free time, and a really good GPS from Sergeant Bub’s Army Surplus store. I’ve got only one problem. The United States is a big place, and no matter how much free time I have, I’m still only one person with a sleeping bag and a video camera. If I simply head to the nearest mountains and pitch my tent, the odds of me spotting a giant ape-man are about the same as the odds of me winning the lottery (and I don’t play the lottery). No, I need to do better than put myself in the woods and hope for the best. But how will I do this? How will I ever prove Bigfoot exists?

Getting Good Data: Why It Pays to Be a Control Freak

It’s too late to get my job back, and my husband isn’t taking my calls, so it seems I have no choice but to continue my search. I decide I’m going to do it right. I may never find the proof I’m looking for, but I’ll give it my best, m...