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Thinking about Statistics

Posted 7/27/2015

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  I was never a math person, and that has changed only minimally as I have gone on with life. I have learned that I am smart enough to figure almost anything out, and I suspect that a different culture (meaning one that was more supportive and positive about women in math and the sciences) would have made a difference to me in high school. But the fact remains that I would surely fail the geometry part of the SAT if I took it now (and an interesting aside: a journalist friend wrote an article about this some years ago. In preparation for his essay, he studied for the SATs and then retook the test in his early 50s. He did almost exactly the same as he had at age 17.) This is relevant, or slightly relevant, as we consider cancer statistics. (and I did well in statistics in college)

  The bottom line, as we are reminded over and over, is that statistics apply to a large group of people; they don't have much to say about any one person's situation. Another reminder about statistics is that the chance remains the same with each coin flip or each genetic inheritance; it will always be 50/50. Many of us avoid statistics, not wanting to know what our chances of staying well look like on paper. Others want all the information that is available and delve deeply into articles and graphs and charts as treatment decisions are made. Once the decisions are made, however, I strongly recommend that we all leave the statistic-obsessing behind. It rarely helps.

  These are two interesting articles about this from Cancer Net. I give you the beginnings and then the links.

Cancer by the Numbers
July 16, 2015 · Kat Caverly

Our intuition fails us when we start thinking about the risk of getting cancer. We’re just
not good with numbers. The current statistic that is often batted around is that one in
two of us will get a diagnosis of cancer during our lifetime. That’s like flipping a coin.
There’s a 50% chance of it coming up heads or tails.
So with cancer we are just as likely to get cancer as to not get cancer? What does that tell us? Not much.
I was diagnosed with invasive breast cancer in 2013. I still am at risk for developing another breast cancer, as unfair as that seems to me. In general, women in the United States have a 12.3% risk of hearing the words, “You have breast cancer” during their lifetime, according to the American Cancer Society, so that’s a 1 in 8 chance, right?
A friend told me this story: She was talking with seven other women, and they were wondering which of them would get breast cancer. I laughed because this personalization of statistical information is a common error when we think about the numbers. I told her, “Well, just include me in the group, and the rest of you won’t have to worry anymore!”
They had been considering their group of eight as if they had an eight-chamber revolver loaded with one bullet and then all had to play Russian roulette. But risk doesn’t work that way. Each woman has the same risk, 12.3% each.

Understanding Statistics Used to Estimate Risk and Recommend Screening

Key Messages
Statistics are used to help doctors understand who is at risk for cancer.
Several types of statistics are used to determine cancer risk for large groups of people: incidence, prevalence,and mortality.
Understanding your risk of cancer can help you receive appropriate screening tests and make lifestyle choices to lower your cancer risk.
Many people may want to know their individual risk of being diagnosed with cancer. Statistics are used to determine the risk of cancer for groups of people and are often helpful to estimate your risk of cancer based on individual aspects that are similar to the groups at risk. However, statistics cannot tell you if you will develop cancer. Read below to learn more about the types of statistics used to estimate cancer risk.


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