1

Where Do Data Come From? 3

Case Study 3 Talking about data: Individuals and variables 4 Observational studies 7 Sample surveys 8 Census 11 Experiments 12 Statistics in Summary 14 Link It 14 Case Study Evaluated 15 LaunchPad Online Resources 15 Check the Basics 15

Chapter 1 Exercises 17

Exploring the Web 20

2

Samples, Good and Bad 21

Case Study 21 How to sample badly 21 Simple random samples 24 Can you trust a sample? 30 Statistics in Summary 31 Link It 31 Case Study Evaluated 32 LaunchPad Online Resources 32 Check the Basics 32

Chapter 2 Exercises 33

Exploring the Web 38

3

What Do Samples Tell Us? 39

Case Study 39 From sample to population 40 Sampling variability 41 Margin of error and all that 45 Confidence statements 47 Sampling from large populations 49 Statistical Controversies: Should Election Polls Be Banned? 50 Statistics in Summary 51 Link It 52 Case Study Evaluated 52 LaunchPad Online Resources 52 Check the Basics 53

Chapter 3 Exercises 54

Exploring the Web 62

4

Sample Surveys in the Real World 63

Case Study 63 How sample surveys go wrong 64 Sampling errors 64 Nonsampling errors 66 Wording questions 70 How to live with nonsampling errors 72 Sample design in the real world 72 The challenge of Internet surveys 76 Statistical Controversies: The Harris Online Poll 78 Probability samples 79 Questions to ask before you believe a poll 80 Statistics in Summary 81 Link It 82 Case Study Evaluated 82 LaunchPad Online Resources 82 Check the Basics 82

Chapter 4 Exercises 83

Exploring the Web 91

5

Experiments, Good and Bad 93

Case Study 93 Talking about experiments 93 How to experiment badly 95 Randomized comparative experiments 98 The logic of experimental design 101 Statistical significance 103 How to live with observational studies 104 Statistics in Summary 106 Link It 107 Case Study Evaluated 107 LaunchPad Online Resources 107 Check the Basics 108

v

Chapter 5 Exercises 109

Exploring the Web 115

6

Experiments in the Real World 117

Case Study 117 Equal treatment for all 117 Double-blind experiments 118 Refusals, nonadherers, and dropouts 120 Can we generalize? 122 Experimental design in the real world 124 Matched pairs and block designs 126 Statistical Controversies: Is It or Isn’t It a Placebo? 130 Statistics in Summary 130 Link It 131 Case Study Evaluated 131 LaunchPad Online Resources 132 Check the Basics 132

Chapter 6 Exercises 133

Exploring the Web 140

7

Data Ethics 141

Case Study 141 First principles 141 Institutional review boards 143 Informed consent 144 Confidentiality 145 Clinical trials 147 Statistical Controversies: Hope for Sale? 151 Behavioral and social science experiments 151 Statistics in Summary 153 Link It 154 Case Study Evaluated 154 LaunchPad Online Resources 154 Check the Basics 154

Chapter 7 Exercises 155

Exploring the Web 162

8

Measuring 163

Case Study 163 Measurement basics 163 Know your variables 165 Measurements, valid and invalid 166 Statistical Controversies: SAT Exams in College Admissions 171 Measurements, accurate and inaccurate 171 Improving reliability, reducing bias 174 Pity the poor psychologist 176 Statistics in Summary 178 Link It 179 Case Study Evaluated 179 LaunchPad Online Resources 180 Check the Basics 180

Chapter 8 Exercises 181

Exploring the Web 186

9

Do the Numbers Make Sense? 187

Case Study 187 What didn’t they tell us? 187 Are the numbers consistent with each other? 188 Are the numbers plausible? 190 Are the numbers too good to be true? 191 Is the arithmetic right? 191 Is there a hidden agenda? 194 Statistics in Summary 196 Link It 196 Case Study Evaluated 197 LaunchPad Online Resources 197 Check the Basics 197

Chapter 9 Exercises 198

Exploring the Web 202

10

Graphs, Good and Bad 215

Case Study 215 Data tables 215 Types of variables 218 Pie charts and bar graphs 218 Beware the pictogram 222 Change over time: Line graphs 223 Watch those scales! 226 Making good graphs 229 Statistics in Summary 231 Link It 232 Case Study Evaluated 232 LaunchPad Online Resources 232 Check the Basics 233

Chapter 10 Exercises 234

Exploring the Web 242

11

Displaying Distributions with Graphs 243

Case Study 243 Histograms 243 Interpreting histograms 247 Stemplots 253 Statistics in Summary 255 Link It 256 Case Study Evaluated 256 LaunchPad Online Resources 256 Check the Basics 257

Chapter 11 Exercises 258

Exploring the Web 266

12

Describing Distributions with Numbers 267

Case Study 267 Median and quartiles 268 The five-number summary and boxplots 272 Statistical Controversies: Income Inequality 275 Mean and standard deviation 277 Choosing numerical descriptions 281 Statistics in Summary 283 Link It 284 Case Study Evaluated 284 LaunchPad Online Resources 285 Check the Basics 285

Chapter 12 Exercises 286

Exploring the Web 292

13

Normal Distributions 293

Case Study 293 Density curves 295 The center and variability of a density curve 296 Normal distributions 298 The 68–95–99.7 rule 300 Standard scores 302 Percentiles of Normal distributions^* 304 Statistics in Summary 306 Link It 307 Case Study Evaluated 308 LaunchPad Online Resources 308 Check the Basics 308

Chapter 13 Exercises 309

Exploring the Web 314

14

Describing Relationships: Scatterplots and Correlation 315

Case Study 315 Scatterplots 317 Interpreting scatterplots 320 Correlation 323 Understanding correlation 325 Statistics in Summary 328 Link It 328 Case Study Evaluated 329 LaunchPad Online Resources 329 Check the Basics 330

Chapter 14 Exercises 330

Exploring the Web 338

15

Describing Relationships: Regression, Prediction, and Causation 339

Case Study 339 Regression lines 340 Regression equations 342 Understanding prediction 344 Correlation and regression 345 The question of causation 348 Statistical Controversies: Gun Control and Crime 352 Evidence for causation 352 Correlation, prediction, and big data 353 Statistics in Summary 355 Link It 355 Case Study Evaluated 356 LaunchPad Online Resources 356 Check the Basics 357

Chapter 15 Exercises 357

Exploring the Web 366

16

The Consumer Price Index and Government Statistics 367

Case Study 367 Index numbers 368 Fixed market basket price indexes 369 Using the CPI 370 Understanding the CPI 374 Statistical Controversies: Does the CPI Overstate Inflation? 376 The place of government statistics 377 The question of social statistics 379 Statistics in Summary 380 Link It 380 Case Study Evaluated 381 LaunchPad Online Resources 381 Check the Basics 381

Chapter 16 Exercises 382

Exploring the Web 387

17

Thinking about Chance 405

Case Study 405 The idea of probability 405 The ancient history of chance 408 Myths about chance behavior 409 Personal probabilities 415 Probability and risk 417 Statistics in Summary 418 Link It 419 Case Study Evaluated 419 LaunchPad Online Resources 420 Check the Basics 420

Chapter 17 Exercises 421

Exploring the Web 425

18

Probability Models 427

Case Study 427 Probability models 427 Probability rules 429 Probability and odds 431 Probability models for sampling 432 Statistics in Summary 435 Link It 436 Case Study Evaluated 436 LaunchPad Online Resources 436 Check the Basics 437

Chapter 18 Exercises 437

Exploring the Web 443

19

Simulation 445

Case Study 445 Where do probabilities come from? 446 Simulation basics 447 Thinking about independence 450 More elaborate simulations 452 Statistics in Summary 455 Link It 456 Case Study Evaluated 456 LaunchPad Online Resources 456 Check the Basics 456

Chapter 19 Exercises 457

Exploring the Web 463

20

The House Edge: Expected Values 465

Case Study 465 Expected values 465 The law of large numbers 469 Thinking about expected values 470 Statistical Controversies: The State of Legalized Gambling 471 Finding expected values by simulation 472 Statistics in Summary 473 Link It 473 Case Study Evaluated 473 LaunchPad Online Resources 474 Check the Basics 474

Chapter 20 Exercises 475

Exploring the Web 480

21

What Is a Confidence Interval? 493

Case Study 493 Estimating 494 Estimating with confidence 495 Understanding confidence intervals 499 More on confidence intervals for a population proportion^* 502 The sampling distribution of a sample mean^* 505 Confidence intervals for a population mean^* 508 Statistics in Summary 509 Link It 510 Case Study Evaluated 511 LaunchPad Online Resources 511 Check the Basics 511

Chapter 21 Exercises 512

Exploring the Web 519

22

What Is a Test of Significance? 521

Case Study 521 The reasoning of statistical tests of significance 522 Hypotheses and P-values 524 Statistical significance 528 Calculating P-values^* 529 Tests for a population mean^* 531 Statistics in Summary 535 Link It 536 Case Study Evaluated 536 LaunchPad Online Resources 537 Check the Basics 537

Chapter 22 Exercises 538

Exploring the Web 545

23

Use and Abuse of Statistical Inference 547

Case Study 547 Using inference wisely 547 The woes of significance tests 550 The advantages of confidence intervals 554 Significance at the 5% level isn’t magical 555 Statistical Controversies: Should Hypothesis Tests Be Banned? 555 Beware of searching for significance 556 Inference as decision^* 557 Statistics in Summary 562 Link It 562 Case Study Evaluated 563 LaunchPad Online Resources 563 Check the Basics 563

Chapter 23 Exercises 564

Exploring the Web 569

24

Two-Way Tables and the Chi-Square Test^* 571

Case Study 571 Two-way tables 572 Inference for a two-way table 574 The chi-square test 577 Using the chi-square test 581 Simpson’s paradox 584 Statistics in Summary 586 Link It 586 Case Study Evaluated 587 LaunchPad Online Resources 587 Check the Basics 588

Chapter 24 Exercises 589

Exploring the Web 594