With this new-found, wide-based exposure to RF energy, fears of ill effects have grown. Over time, as studies have been performed on the health of the newly exposed population, most have shown no increase in disease; however, the concern is that "more studies must be done," because the length of exposure of cellular telephone users may be too short to reveal diseases that take a long time to occur.

Miners in the old days would take canaries with them deep into mines. The small bird was an indicator of problems with the air quality, its demise serving to warn the miners to get out of the mine before the air got bad enough to injure a human.

Radio amateurs are arguably the largest group in our society with the highest exposure to RF for the longest time. Like canaries in mines, studying the health of radio amateurs in reference to the general population could be used to warn the rest of the population if RF exposure can cause disease.

This was the motivation behind the epidemiological study of radio amateurs by Samuel Milham in the mid-1980s. This study of the death records of a relatively small group of California and Washington State hams purported to show a very weak relationship between being a radio amateur and one form of leukemia; however, the study was far too limited to be used to draw any conclusions (for more information, please see N9GL's RF Safety Column, "They Blinded Me With Science," April 2000,).

The health records of hams are too valuable a resource to be ignored -- a more comprehensive study of hams would still make a valuable addition to the science of public health. As such, around the year 2000, the National Cancer Institute (NCI) -- one of the National Institutes of Health (NIH) -- undertook a new epidemiological study of radio amateurs (see "Researcher Undertaking Epidemiological Study of Radio Amateurs").

Epidemiologists at NCI studied 108,586 subjects who held Amateur Radio licenses and who had lived in California any time from 1966-1995. California death records, the National Death Index and the Social Security Administration mortality listings were used to track which of these people had died, resulting in 1,734,930 person-years of study.

This group was subdivided into subgroups based on license class, with the expectation that high license classes indicated more intense activity on the radio and a likelihood of employment in broadcasting or electronics industries. Deaths were compared to standard population death rates, subdivided by disease and results were expressed as SMRs, or Standard Mortality Ratios. An SMR of 1.0 means that the test group has the same rate of death from a particular cause as the standard population. An SMR of 2.0 means that the test group is twice as likely to die from a particular cause than the standard population, and an SMR of 0.5 means that the test group is half as likely to die from a particular cause than the standard population.

Because these are statistical calculations, a 95 percent confidence interval is also calculated for each SMR. Thus, an SMR of 2.0 with a confidence interval of 1.0-3.0 means that the test group appears to be twice as likely to die of a disease than the standard population, but the uncertainty of the numbers is such that the SMR could have been anywhere between 1.0 and 3.0. Such a result is not considered to be statistically significant because 1.0 is within the 95 percent confidence limits.

The relevant results from the first phase of the study are as follows:

• Cancer Deaths: 0.79 (0.76-0.81) -- this is a significant result that hams are less likely to die of any of the many types of cancer than the standard population.
  

• Glioma Deaths: 1.14 (0.97-1.30) -- this is a non-significant result that hams appear to be slightly more likely to die of this type of brain tumor than the standard population.
  

• Leukemia Deaths: 0.89 (0.80-1.03) -- this is a non-significant result that hams appear to be slightly less likely to die from any form of leukemia (blood cancer) than the standard population.
  

• Chronic Myelogenous Leukemia Deaths: 1.2 (0.90-1.70) -- this is a non-significant result that hams appear to be slightly more likely to die from this specific form of leukemia than the standard population.
  

• Hodgkin's Disease Deaths: 1.3 (0.90-1.90) -- this is a non-significant result that hams appear to be slightly more likely to die from this form of lymphatic cancer than the standard population.
  

• ALS Deaths: 1.21 (0.90-1.60) -- this is a non-significant result that hams appear to be slightly more likely to die from this form of nervous system degeneration (Lou Gehrig's disease) than the standard population.
  

• Laryngeal Cancer Deaths: 0.60 (0.40-0.80) -- this is a significant result that hams are less likely to die from this often smoking-related disease than the standard population.
  

• Lung Cancer Deaths: 0.65 (0.61-0.69) -- this is a significant result that hams are less likely to die from this disease, which is also most often related to smoking, than the standard population.
  

If the average numbers are taken at face value without considering the statistical uncertainties, there are four of the above diseases that hams appear to incur more often than the rest of the population, no matter how slight the increase. The same set of numbers also could imply that ham radio protects people from four other diseases. In fact, even though none of the increased rates of disease is statistically significant, three of the apparent protective effects are statistically significant.

As with the Milham study, the NCI study is highly preliminary. It does not consider any of the many other factors that affect the onset of disease. There was no information obtained for either study that took into account health factors such as smoking habits, the general health of the subjects including weight, diet and exercise, family disease histories and occupational factors. Also, neither study confirmed the amount or type of exposure each licensed ham had to RF. Were they operators who used QRP or QRO, UHF or VLF, an HT or an antenna on a 100 foot tower?

Just as it defies logic that simply being a radio amateur protects one from getting laryngeal cancer or lung cancer, the results above clearly do not support any implication that being a radio amateur increases the risk of glioma, leukemia, Hodgkin's disease or ALS. Clearly, based on this analysis, we hams are not dropping dead because we enjoy our hobby.

Epidemiological studies are fairly expensive to perform. From results such as those listed above, it is hard to make the case that much additional money should be spent to obtain the information that would make the results more conclusive. From preliminary studies such as these, it often takes SMR values of 5.0 or greater to justify more research to improve the specificity of the results.

The epidemiologists at NCI are continuing to subdivide the sample population on which they have already collected information. They are using additional statistical techniques to try to glean more conclusions from these data. To date, the cry to get out of the mine does not appear to be forthcoming.

We as hams can be proud that our experience in our hobby is providing scientists with valuable information that directly benefits public health policy. We should be proud to be the canaries in the mine.

Greg Lapin, N9GL, started working in the RF safety world after spending many years first studying cardiac function imaging and then brain tumor kinetics. He serves as chairman of the ARRL RF Safety Committee and as a member of the FCC Technological Advisory Council. A former professor of Biomedical Engineering and Neurology at Northwestern University, Lapin now works as a consulting professional engineer in the electronics industry. He was first licensed while a teenager in 1969 and continues to be fascinated by virtually all aspects of Amateur Radio. One of his many interests is electronic design, and he is the author of Chapter 8, "Analog Signal Theory and Components" in The ARRL Handbook for Radio Amateurs. His non-ham interests include making things grow in his garden and serving as commissioner of the local children's softball league. At other times -- when he is not working or helping his kids with their homework -- you might find him with the local emergency services agency, climbing his tower, building a new QRP rig, playing with his APRS setup, responding to QSL cards, going off on a DXpedition or trying to get that "new one." You can reach him via e-mail at g.lapin@ieee.org. The ARRL RF Safety Committee page contains a link to archives of previously posted editions of N9GL's RF Safety Column.

Gregory Lapin, PhD, PE, N9GL
Chairman, ARRL RF Safety Committee