I have drawn on the following works: Last, J. L., Dictionary of Epidemiology (2001) (JL); Gordis, L., Epidemiology, 2004 (LG); National Research Council, Health Effects of Exposure to Radon, BEIR VI, 1999 (BEIR VI); and Wikipedia (W); initials in parenthesis indicate direct quotes or paraphrases from these sources.
absolute risk: The probability of an event in population under study, as contrasted with the relative risk (JL).
action level: Upper limit on radon concentration in homes, above which the EPA recommends action to reduce the level. The EPA has set an action level of 4 pCi/L of air.
Georgius Agricola (Latinized name of Georg Bauer) (1494–1555): Sixteenth-century German scholar and scientist known as the “father of mineralogy” for his systematic treatise on mining and metallurgy De re metallica, published posthumously in 1556. Agricola noted the occurrence of an unusually high death rate from lung disease among underground metal miners in the Erz Mountains spanning Germany and Czechoslovakia (W; BEIR VI).
alpha particle: Two neutrons and two protons bound as a single particle that is emitted from the nucleus of certain radioactive isotopes in the process of decay or disintegration (BEIR VI).
association: A correlation between an exposure or a characteristic and a disease. Association is a necessary condition of a causal relationship, but many phenomena are associated without one of them causing the other. Hence, the dictum “association does not prove causation.”
“availability heuristic”: Term coined by the psychologists Daniel Kahneman and Amos Tversky to describe the phenomenon that people’s judgment about the likelihood, and hence the importance, of an event is influenced by salient events and experiences that make a strong impression but lead to systematic errors. Kahneman won the Nobel Prize for this work in 2002.
becquerel per meter cubed (Bq/m3): The concentration of radon in the air is measured in units of becquerels per meter cubed or in picocuries per liter (pCi/L) of air. One picocurie per liter is equivalent to 37 Bq/m3. One becquerel corresponds to 1 disintegration per second.
bias: Deviation of results or inferences from the truth or processes leading to such deviation. Any trend in the collection, analysis, interpretation, or review of data that can lead to conclusions that are systematically different from the truth (JL).
biological marker, or biomarker: A cellular or molecular indicator of exposure, health effects, or susceptibility. Biomarkers can be used to measure internal dose, biologically effective dose, early biological response, altered structure or function, or susceptibility (JL).
BRCA1 and BRCA2: Rare mutations in genes that cause a greatly increased risk of breast and several other cancers in some families. Such mutations account for only a few percent of breast cancers.
case-control study: Type of study in which cases of a particular disease are identified and a comparison group without the disease (controls) are identified. Information on factors thought to play a role in the disease is obtained from both groups and compared. Case-control studies are particularly useful in studying uncommon diseases.
causality: The relating of causes to the effects they produce. Most epidemiology concerns causality, and several different types of causes can be distinguished. It must be emphasized, however, that epidemiologic evidence by itself is insufficient to establish causality, although it can provide powerful circumstantial evidence (JL).
cohort study: Study in which information relevant to the risk of developing disease is collected from members of a defined population or “cohort.” The cohort is then followed for a number of years, and cases (or deaths) of the disease of interest are identified. Factors that are associated with the development of the disease can then be evaluated.
concentration: The level of a substance present in a particular environment or in a biological specimen such as blood. For radon, picocuries per liter of air and becquerels per meter cubed are used; for environmental tobacco smoke, common measurements are in micrograms of particles or nicotine per cubic meter of air (a microgram is one millionth of a gram). Concentration is to be distinguished from exposure.
confidence interval: A measure of the reliability of a risk estimate. A 95 percent confidence interval means that 95 times out of 100 the estimated risk will fall within the specified interval.
confounding, confounding factor: Refers to the distortion of an observed association between the factor of interest and a disease by a third factor that is associated with both the study factor and the disease.
congeners (PCB congeners): Structurally similar forms of a compound.
cotinine: A major metabolite of nicotine that can be measured in blood, urine, or saliva. Cotinine levels reflect smoking in the previous 2 days.
criteria of judgment: Set of guidelines that are useful in assessing whether an association is likely to be causal. These include the strength of the association, the consistency of the association observed in different studies, temporality (whether the exposure precedes the occurrence of disease), and biological plausibility.
dichloro-diphenyl-trichloroethane (DDT): Synthetic pesticide widely used in agriculture following World War II. In her 1962 book Silent Spring, the biologist Rachel Carson drew attention to the effects of indiscriminate use of DDT on wildlife and possibly human health. DDT was banned for most uses in 1972.
DNA adduct: The result of a toxin’s binding to the genetic material and causing damage, which, if not repaired, can theoretically lead to cancer.
dose-response relationship: Refers to change in the risk of disease (response) as exposure to the factor of interest (dose) increases. The stronger the dose response seen between a factor and a disease, the more likely it is that the factor causes the disease. The number of cigarettes smoked per day by smokers shows a classic dose-response relationship with their risk of lung cancer.
ecological study: Study in which information pertaining to populations is correlated with the occurrence of disease.
electric fields: Produced by voltage and are measured in volts per meter. Electric fields are easily shield by trees and buildings.
electromagnetic spectrum: The range of all possible electromagnetic radiation from gamma rays, with very high frequencies and energies, to extremely low frequency power frequency fields that have very low energy levels.
ELF-EMF (extremely low frequency electromagnetic fields): Produced by electric power lines are below 3,000 Hz and have wavelengths of more than 5,000 km.
environmental tobacco smoke (ETS): Mixture of smoke from the burning tip of a cigarette and the smoke exhaled by the smoker. Synonymous terms include “passive smoking,” “secondhand tobacco smoke,” and “involuntary smoking.”
etiology: Science or description of the causes of disease.
excess relative risk: Risk due to exposure to a certain level above the background level.
exposure: The condition of having contact with a physical or chemical agent in such a way that the contact can influence the development of disease.
hertz:Unit of frequency expressed in cycles per second. Frequency is proportional to energy level of electromagnetic radiation and inversely proportional to its wavelength.
Human Genome Project: A 13-year project coordinated by the U.S. Department of Energy and the National Institutes of Health in collaboration with scientists in other countries to identify all of the approximately 20,000–25,000 genes in human DNA and determine the sequences of the 3 billion chemical base pairs that make up human DNA. The project was completed in 2003.
incidence: The number of new cases of a disease within a specified period of time.
information bias: Flaw in measuring exposure or outcome data that results in different quality (accuracy) of information between comparison groups (JL). In a case-control study, the information obtained from cases may be affected by the fact of their having received a diagnosis of a serious illness. This may have prompted them to reflect more intensively on their past exposures in an attempt to account for their illness. Healthy controls have do not have the same incentive.
interaction: The phenomenon of two exposures acting jointly to increase risk to a greater extent than either exposure alone; synergism.
ionizing radiation: Electromagnetic radiation with sufficient energies to dislodge electrons from an atom, thereby producing an ion pair. Ionizing radiation includes X-rays and gamma rays, and alpha particles, which can damage DNA through ionization.
Koch’s postulates: Formulated by F. G. Jacob Henle and adapted by Robert Koch in 1877 for use in determining whether a particular microorganism was the cause of a specific disease. (1) The agent must be shown to be present in every case of the disease in pure culture; (2) the agent must not be found in cases of other disease; (3) once isolated, the agent must be capable of producing the disease in experimental animals; and (4) the agent must be recovered from the experimental disease produced (JL).
latency, latent period: Period between the onset of exposure and the appearance of clinically detectable disease. In the case of chronic diseases, the latency period can range from several years to decades.
linear-no-threshold (LNT) model: A model of the damage caused by ionizing radiation which presupposes that the response is linear (i.e., directly proportional to the dose) at all dose levels. Thus LNT asserts that there is no threshold of exposure below which the response ceases to be linear (W).
magnetic fields: Produced by current flowing in wires. Magnetic fields are not easily shielded. Measured in gauss (G) or tesla (T).
meta-analysis: A technique used to combine the results of a number of small studies in order to obtain a summary estimate, which, it is hoped, will better describe the true relationship. Meta-analysis can be carried out using the data available in published papers, in contrast to pooled analyses, which involve reanalyzing the original data from different studies using a common approach.
microtesla(µT): Measure of magnetic fields (specifically flux density). One microtesla is equivalent 10 milligauss.
milligauss(mG): Measure of magnetic fields (flux density). One milligauss = 0.1 microteslas.
misclassification: The erroneous classification of an individual, a value, or an attribute into a category other than that to which it should be assigned. The probability of misclassification may be the same in all study groups (nondifferential misclassification) or may vary between groups (differential misclassification) (JL).
odds ratio: The measure of association obtained from a case-control study, compares the “odds” of exposure to the factor of interest among the cases to the odds of exposure among the controls.
organochlorine compounds: Class of compounds including DDT, heptachlor, chlordane, mirex, and PCBs (polychlorinated biphenyls).
PAH (polycyclic aromatic hydrocarbon):Class of compounds produced by combustion of fossil fuels and other organic matter.
Paracelsus(adopted name of Philippus Theophrastus Aureolus Bombastus von Hohenheim) (1493–1541): Sixteenth-century Swiss alchemist and physician who wrote, “All things are poison and nothing is without poison, only the dose permits something not to be poisonous.” Paracelsus pioneered the use of chemicals and minerals in medicine and engaged in experimentation to learn about the human body. He believed that sickness and health were dependent on the balance of specific minerals and that certain illnesses had chemical remedies that could cure them. Like his contemporary, Agricola, he wrote a major work on mining, On the Miners’ Sickness and Other Diseases of Miners, in which he documented the occupational hazards of metalworking as well as treatment and prevention strategies (W).
picocurie: One trillionth of a curie. A curie is the amount of radioactivity emitted by the decay of a gram of radium. Picocuries per liter of air (pCi/L) is a measure of radon concentration or level in a given environment.
polychlorinated biphenyls (PCBs): Class of organic compounds that are no longer produced the United States but are still found in the environment. PCBs were widely used in the electrical and other industries, but were banned in the 1970s due to their toxicity.
pooled analysis: The collaborative reanalysis of data from a number of studies using a common analytic approach.
prevalence:Frequency of occurrence of a factor in the population.
prospective study: Another term for a cohort study.
radiation: Energy emitted in the form of waves or particles by radioactive atoms as a result of radioactive decay (BEIR VI).
radionuclide: An atom with an unstable nucleus, which undergoes radioactive decay, emiting ionizing radiation. (BEIR VI).
radon:A naturally occurring radioactive gas produced by the decay of radium, which in turn is produced by the decay of uranium; decays to form radon progeny (or radon “daughters”) (BEIR VI).
radon progeny or daughters: The radioactive products formed following the radioactive decay of radon; radionuclides which when inhaled can expose living cells to their emitted alpha particles (BEIR VI).
Ramazzini, Bernadino(1633–1714): Seventeenth-century Italian physician and founder of the field of occupational medicine. He was an early proponent of the use of cinchona bark (from which quinine is derived) in the treatment of malaria. His most important contribution to medicine was his work on occupational diseases called De Morbis Artificum Diatriba (Diseases of Workers) which outlined the health hazards of chemicals, dusts, metals, and other agents encountered by workers in fifty-two occupations (W). In this work, he noted that breast cancer occurred more often in nuns then in the general population of women and speculated that some aspect of childbearing might be protective.
relative risk: The ratio of the risk of disease or death among the exposed to the risk among the unexposed (JL).
risk: The probability that an event will occur, e.g., the probability that an individual will become ill or die within a stated period of time or by certain age. Also a nontechnical term encompassing a variety of measures of the probability of a (generally) unfavorable outcome (JL).
risk factor: A personal characteristic or exposure that in an epidemiologic study is associated with the occurrence of disease. The characteristic could be a sociodemographic factor (such as age, sex, ethnicity), a clinical characteristic (cholesterol level), an exposure, or a genetic factor. Often the term is used to imply a causal relationship, when this is not appropriate. Age is a strong risk factor for colon cancer and many other diseases, but age is not a cause of colon cancer. It is more appropriate to interpret “risk factor” to mean “risk marker.”
selection bias: Error due to systematic differences in characteristics between those who take part in a study and those who do not. Selection bias can invalidate conclusions and generalizations that might otherwise be drawn from such studies (JL).
selective estrogen receptor modulators (SERMs): A class of drugs that act on the estrogen receptor to selectively inhibit or stimulate estrogen-like action in various tissues. Tamoxifen and raloxifene are examples of SERMs.
statistical significance: A measure of whether a particular result is unlikely to be due to chance. If the 95 percent confidence interval associated with a relative risk does not include 1.0, the result is judged to be statistically significant.
tesla: Measure of magnetic fields, specifically of magnetic flux density. One tesla is equivalent to 10,000 gauss (G). Magnetic fields in homes are measured in microTesla, or µT.
threshold: Level below which an agent or toxin has no adverse effect.
working level (WL): Measure of the concentration of radon daughters, which is a measure of the potential alpha particles energy per liter of air. One WL of radon daughters corresponds approximately to a level of 200 pCi/L of radon in a typical indoor environment.
working level months (WLM): A measure of cumulative exposure to radon used in studies of miners and equivalent to 1 working level for a working month (170 hr) (BEIR VI).