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Woloshin S, Schwartz LM, Welch HG. Know Your Chances: Understanding Health Statistics. Berkeley (CA): University of California Press; 2008.

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Know Your Chances: Understanding Health Statistics.

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Chapter 3Risk Charts

A Way to Get Perspective

How does a specific risk compare to other risks for your age group and your gender? Answering this question is precisely the purpose of our risk charts. Because the risk charts are so important to understanding risk and providing perspective, we want you to take a close look at them. (The full charts appear in the Extra Help section at the end of the book, pages 128—129.)

We created two risk charts: one for men and one for women. The columns in the charts indicate various causes of death. Each chart shows the 10-year chance of dying from these causes for people of different ages. There are two rows of numbers for each age: the rows in regular type are for people who have never smoked (individuals who don't smoke now and who have smoked fewer than 100 cigarettes in their lifetime, referred to in the charts as “never smoked”), and the rows in bold type are for people who currently smoke (individuals who have smoked at least 100 cigarettes and who smoke now).

Why do we give separate numbers for current smokers and people who never smoked? It’s because smoking has such a strong influence on your risk of dying. You probably know that smoking causes lung cancer. But smoking also makes a big difference when we look at many other diseases, such as heart attack, stroke, and pneumonia.

To highlight how much smoking matters, let’s take a look at part of the chart for women.

Find the line with a specific age and smoking status. The numbers in that row tell you how many out of 1,000 women in that group will die in the next 10 years from . . .

AgeSmoking StatusVascular DiseaseCancerInfectionLung DiseaseAccidentsAll Causes Combined
Heart AttackStrokeLungBreastColonOvarianCervicalPneumoniaFluAIDSCOPD
50Never smoked411411237
Smoker1351441114269
55Never smoked822622111255
Smoker206265221192110

Note: Shaded portions mean that the chance is less than 1 out of 1,000. COPD is chronic obstructive pulmonary disease, which includes emphysema and chronic bronchitis.

In the chart, find the rows for 50-year-old women. For women who never smoked, the chance of dying in the next 10 years from all causes combined is 37 out of 1,000. (Note that this is the same row of data we used in chapter 2.) For current smokers, the corresponding risk is almost twice as high: 69 out of 1,000.

What about former smokers? Things are a little more complicated for them. That’s because risks for smoking-related diseases drop after you quit smoking. But it’s hard to say how much the risks drop. Your change in risk depends mostly on two basic factors: how much you smoked (when you started and how many cigarettes you smoked each day), and how long it’s been since you quit. If you are a former smoker, you can also use the risk charts: your risk falls somewhere between that of current smokers and people who never smoked. The longer it’s been since you smoked and the less you smoked, the closer your risk is to that of people who never smoked. And the more you smoked and the more recently you quit, the closer your risk is to that of current smokers.

As you examine the charts in the Extra Help section, you should notice a number of things. Looking across the rows lets you compare the chances of dying from different causes at a given age. This helps to put each cause of death in perspective—for example, you can see how the chance of dying from a heart attack compares to the chance of dying from lung cancer or to the chance of dying from all causes combined. Looking down the columns, you can see how risk changes with age. For most causes, the chance of dying increases steadily with age. So don’t just focus on one number—look at the numbers around it, too.

Finally, by comparing the numbers for current smokers and people who never smoked, you can get a good sense of how much smoking increases your chance of dying. As you’ll see, smoking makes a really big difference for some risks. For both men and women, at all ages, smoking greatly increases the chance of dying from heart attack, lung cancer, COPD, and all causes combined; it increases the chance of death from stroke and pneumonia too, but to a lesser extent.

In other cases, such as accidents or prostate cancer or AIDS, smoking does not make a difference. This makes sense: there is no biological reason that smoking would affect these causes. But if you look at the charts carefully, you’ll see that smokers are a little less likely to die from some causes than people who never smoked. For example, the chance of a 75-year-old man dying from prostate cancer in the next 10 years is 19 in 1,000 for men who never smoked, but only 15 in 1,000 for men who currently smoke. Does that mean smoking protects you from prostate cancer? No, these small differences reflect the fact that these men die from only one cause—and since smoking increases their chance of dying from something like a heart attack or lung cancer (by a lot), that leaves fewer men to die from causes such as prostate cancer.

For smoking, the message is clear: it really increases your chance of dying. In fact, being a current smoker has the same effect on the risk of death from all causes combined as adding about 5 to 10 years of age. For example, the risk of death for a 55-year-old man who currently smokes is 178 out of 1,000, about the same as the risk for a 65-year-old who has never smoked (176 out of 1,000).

When you use the charts, be careful to choose the one for your sex. And then be careful to look at the right rows, choosing the one for your age and for whether you have never smoked or smoke now. If you use the wrong chart or look at the wrong rows, you’ll get the wrong information.

Let’s make sure you’re using the charts correctly. For the following quiz, use the full risk charts in the Extra Help section (pages 128–129):

QUIZ

Mr. Jones is a 65-year-old current smoker. What is his chance of dying from lung cancer in the next 10 years?

  1. 4 in 1,000
  2. 55 in 1,000
  3. 89 in 1,000

Mrs. Smith is a 50-year-old who has never smoked. What is her chance of dying from colon cancer in the next 10 years?

  1. 1 in 1,000
  2. 4 in 1,000
  3. 34 in 1,000

Mr. Wilson is a 55-year-old former smoker. He smoked for many years and quit about a year ago. What is his chance of dying from a heart attack in the next 10 years? (Make your best guess here.)

  1. 19 in 1,000
  2. 24 in 1,000
  3. 31 in 1,000
  4. 41 in 1,000
  5. 56 in 1,000

For Mr. Jones, the correct answer is c. Mr. Jones’s chance of dying from lung cancer in the next 10 years is 89 in 1,000. If you answered 4 in 1,000, you looked at the wrong row of the chart (you found the number for men who have never smoked rather than the number for current smokers). If you said 55 in 1,000, you mistakenly used the chart for women who currently smoke.

For Mrs. Smith, the correct answer is a. Mrs. Smith’s chance of dying from colon cancer in the next 10 years is 1 in 1,000. Note that her smoking history didn’t matter—the chance of colon cancer death is not affected by smoking. If you answered 4 in 1,000, you probably looked at the wrong column of the chart (this is her chance of dying from breast cancer).

For Mr. Wilson, the correct answer is c. If Mr. Wilson still smoked, his chance of dying from a heart attack in the next 10 years would be 41 in 1,000. Because he quit, his chance will be lower. But because he smoked for a long time and quit only recently, the chance will still be pretty close to that of a current smoker, so we think the best guess is 31 in 1,000. Answer b (24 in 1,000) is also in the range between the nonsmoker and current smoker risks. But with Mr. Wilson’s long history of smoking and his relatively short smoke-free time, it is unlikely that his risk dropped to this level. If you chose the answer 19 in 1,000, you looked at the row for people who never smoked.

Before you proceed to part two, be sure that you’re comfortable reading the risk charts. These charts put the risk of death in perspective in a number of ways: comparing the chance of death across diseases, at different points in the life span, and in the context of all causes combined. They also send a strong message about how risk is increased by smoking.

Questions to Ask When Interpreting Risk

Throughout these first three chapters, we’ve emphasized the key questions you should ask when you’re trying to make sense of messages about health risks. Here’s a brief summary:

Risk of what? Understand what the outcome is (getting a disease, dying from a disease, developing a symptom), and consider how bad it is.

How big is the risk? Find out your chance of experiencing the outcome. If you hear about the number of people who experience an outcome, always ask, “Out of how many?” You need to know how many people could have experienced the outcome in order to calculate your own chance. Also ask, “What is the time frame?” Is the time frame for the risk the next year, the next 10 years, or a lifetime?

Because there are many ways to express the same risk, it’s useful to put information in a consistent format. Our choice would be “___out of 1,000 people over 10 years.”

To get the full picture, we also suggest that you reframe the risk: for example, if 5 out of 1,000 people will die over 10 years, it is also true that 995 out of 1,000 will not die.

Does the risk information reasonably apply to me? Determine whether the message is based on studies of people like you (people of your age and sex, people whose health is like yours).

How does this risk compare with other risks? Get some perspective by asking about other risks you face so that you can develop a sense of just how big (or small) this particular risk really is.

Copyright © 2008, The Regents of the University of California.

Know Your Chances: Understanding Health Statistics is hereby licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported license, which permits copying, distribution, and transmission of the work, provided the original work is properly cited, not used for commercial purposes, nor is altered or transformed.

Bookshelf ID: NBK126159

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