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Cancer Clusters, Statistics, and Proof

John R. Vig, Ph.D.

Many events that the news media (and others) treat as significant are simply statistical aberrations. Cancer "clusters" often fit this description.

For example, a few years ago, someone noticed that people living on one street in my area had a higher than normal incidence of cancer. Right away, people were suspecting the environment, e.g., the well waters. After lots of tests, nothing unusual was found, but some were still convinced that there was some cause-and-effect relationship between living on that street and the cancer incidence. Some people refuse to believe that such things can happen for no particular reason - i.e., that they may be due to just statistical fluctuations.

If one tosses a coin 10 times, repeatedly, then on the average, there will be five heads and five tails. However, sometimes, there will be seven heads, or eight tails, and, about 1 out of a thousand times (on average), one will get 10 heads (or ten tails). Some may conclude that there is something magical about the coin that came up heads 10 times in a row.

Similarly, the average cancer incidence for each 100 people living in a neighborhood may be one per year (I don't know what the correct number is.) As there are about 250 million people in the USA, there are 2.5 million groups of 100 people. Among these 2.5 million groups, some will have no cancer cases, and others may have 10 cases. The group with zero cases is not necessarily in a safer neighborhood that the group with the 10 cases. There may be nothing special about either the zero incidence group or the group with the 10 cases.

So, the next time you encounter a cancer-related "danger" that is "proven" with statistics, be aware that it may be only a statistical fluctuation. Before acting on what you hear, check with a reliable source, or look for additional evidence that confirms the danger.

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Dr. Vig is a physicist who does research on high-accuracy clocks, frequency standards, and sensors.. He is President of the Ultrasonics, Ferroelectrics and Frequency Control (UFFC) Society of the Institute of Electrical and Electronics Engineers (IEEE) - and operates the UFFC Web site. He resides in and operates the Web site of Colts Neck, New Jersey.

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