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Appendix D Glossary Association: A relationship, generally demonstrated by statistical tests, between an exposure and a health effect. It does not necessarily imply cause and effect. Atexia telangiectasia: An inherited disorder associated with an increased risk of cancer, especially lymphoma, and characterized by immunologic, chromosonal, and DNA defects. Background radiation: The amount of ionizing radiation to which a person is exposed from natural sources, such as terrestrial radiation due to naturally occurring radionuclides in the soil, cosmic radiation originating in outer space, and naturally occurring radionuclides deposited in the body. Becquerel (Bq): The international unit of activity. One becquerel corresponds to 1 disintegration per second, or 2.7 X 10-11 curies (Ci). Under the international system of nomenclature, becquerels are expressed in multiples of 1 thousand. Thus, 1 thousand becquerels, a kilobecquerel, is abbreviated as KBq, 1 million, a megabecquerel, is abbreviated as MBq, and 1 million billion, a petabecquerel, is abbreviated as PBq. Bias: Any process in any stage of the collection or analysis of data that tends to produce results that differ systematically from the ''true value" of the population variables under study (such as disease rates). In epidemiology the term does not refer to an opinion or point of view.
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Biologic marker of effect: A biologic change that is specifically associated with the development of a disease and detectable before the disease is evident. Biologic marker of exposure or dose: Biologic changes that are specifically induced (in this case) by ionizing radiation that can be measured before any health consequences from exposure are evident, and that can be used to quantify radiation dose. Biologic marker of susceptibility: A biologic change that demonstrates a differential susceptibility of specific individuals to genotoxicity from ionizing radiation. Cancer: A general term applied to a variety of diseases characterized by abnormal new growth of tissue and by the spread of that tissue to new sites in the body. Carcinogen: A substance that causes cancer. Case: In epidemiology, a person identified as having a particular health end point (such as a specific disease) under investigation. Case-control study: An epidemiologic investigation that compares exposures in persons who have (cases) or have not (controls) developed the disease under study. Cluster: A series of cases that occur close together in time, location, or both. Normally used to describe a grouping of relatively rare diseases, such as leukemia. Cohort: In epidemiology, a group of persons who are initially free of the disease in question but who have been exposed to the agent under study. The group is followed up, or traced, after a period of time to quantify the occurrence of the disease in the cohort. Confidence interval: A range of values bracketing a relative risk or odds ratio estimate calculated in such a way that the range has a specified probability (usually 95%) of including the true, but unknown, value of the risk. The end points of the confidence interval are called the confidence limits. Confidence limit: See confidence interval. Confounding: A situation in which an observed association between an exposure and a disease is influenced by other variables associated with the exposure that affect the occurrence of disease. Confounding variable (confounder): A variable that could explain an observed association (or lack of an association) in an epidemiologic study between an exposure and a disease. A confounder can create a spurious association between an exposure and a disease or it can mask, weaken, or exaggerate a real association. Confounding must be ruled out before confidence can be placed in any observed association.
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Control: In case-control studies, a person who has not developed the disease of interest and whose exposure is compared with the exposure of those who have. See case-control study. Directed study: Focused selection and analysis of data based on a predetermined method for reconstruction of a source term. Dose dose-rate effectiveness factor (DDREF): A factor by which the effect caused by a specific dose or dose rate of radiation changes at low as compared to high doses or dose rates. Dose validation: The use of direct measurement of radionuclide content in the body, dose in environmental samples, individual dose measurements (physical or biodosimetric) to test the results of model evaluations. If the result of direct measurement is different from model prediction, priority must be given to the measurement. Episodic release: Release of radiation to the environment that is at least 10 times greater than the average amount and for a duration of no more than 10 days. FISH (fluorescence in situ hybridization): The use of DNA libraries derived specifically from particular chromosomes and conjugated with fluorescent molecules to generate reagents that cause distinctive fluorescence on individual chromosomes. Chromosomal aberrations involving the transfer of DNA from one chromosome to another (such as reciprocal translocations) can be detected using this "chromosome painting." Follow-up: The process in which epidemiologists track study subjects to observe variables of interest, such as the occurrence of a specific disease, over time. Genotoxicity: Damage to cellular DNA. Gray (Gy): The international unit for absorbed dose. One gray is equal to 1 joule per kilogram, or 100 rad; therefore, 10 mGy = 1 rad. Latency: The period between exposure to a disease-causing agent and the appearance of symptoms. After exposure to ionizing radiation, for example, there is an average latency of 5 years before leukemia develops, and more than 20 years before some other malignant conditions develop. Leukemia: A disease characterized by rapid and abnormal proliferation of white blood cells in the blood-forming organs (bone marrow, spleen, lymph nodes) and by the presence of immature white blood cells in the peripheral circulation.
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Localization of dose: The evaluation of organ doses or anatomic site-specific doses appropriate to the biologic effect for epidemiologic purposes. For example, the dose from iodine radionuclides to the thyroid is necessary for the study of thyroid cancers. Matched control: In a case-control study, one of a group of persons selected for attributes that are similar to those of persons in the case group. Cases and controls are matched for age, gender, race, or socio-economic status, for example. See case-control study. Matching variable: A characteristic, such as age or gender, used to select controls. See matched controls. Misclassification error: The erroneous classification of a person into a category. In an epidemiologic study of EMF exposure based on job, for example, including some electricians in the "exposed" group might result in misclassification error if those electricians routinely work on dead circuits. Mortality: Death; the number of deaths in a given time or place; the death rate. Mutant: A cell that has been identified as containing DNA with a mutation. Mutation: A change in DNA sequence. Mutation spectra: A description of the different kinds of DNA damage (such as deletions, frame shifts, base substitutions, and inversions) that occur when cells are exposed to mutagenic events. Person-years at risk: A number used as the denominator in incidence and mortality rate calculations; the sum of the years that the persons in the study were observed to see whether they develop the disease or condition of interest. Each person contributes only as many years of observation to the study as he or she is actually observed; if a person leaves, contracts the disease under study, or dies after one year, he or she contributes 1 person-year; if a person leaves after 10 years, he or she contributes 10 person-years. Population: All inhabitants of a given area. Power (statistical): In epidemiology, the probability of concluding that an association between an exposure and a disease exists, when the association does not, in fact, exist. Precision: The closeness of repeated measurements of the same quantity. Proprietary information: Information protected from public disclosure by ownership rights. P-value: See statistical significance.
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Quality of radiation: Epidemiologic analysis must account for the quality of radiation. Dose assessment must be made for each group of radiations with different quality (beta plus gamma radiation, alpha radiation) rad: The unit of radiation absorbed dose, a traditional derived unit defined as the absorption of 100 ergs/gram. Rate: In a population, the number of times a specific event occurs during a specific period. Reference group: A group with which a population under study is compared. Registry: A file of data on all instances of a particular disease in a population, such as all cancer cases in Iowa. With this information, epidemiologists can calculate incidence rates for other groups. Relative risk: A measure of risk based on disease rate or death rate that is used frequently in cohort studies. Relative risk indicates the increased or decreased degree of risk among exposed subjects compared with unexposed persons. A relative risk of 1 indicates no association between the exposure and the disease. A relative risk of 2 indicates that the exposed group is twice as likely as the unexposed group to experience the health effect being studied. Release: A discharge into the environment of radioactive materials either as a result of an accident or in the course of production. Reliability: The degree to which the results of a study can be replicated. Lack of reliability can arise from divergences between observers or instruments of measurement or from the instability of the attribute being measured. rem: The traditional derived unit of dose equivalence equal to the dose in rad multiplied by the quality factor (Q) of the radiation. For x-rays and rays the Q is usually 1 meaning that an exposure to 1 rad is a rem. Retinoblastoma: A malignant embryonic neoplasm of the retina of the eye. Retrospective cohort study: An epidemiologic study that follows a cohort from some time in the past to a more recent time in the past. Existing records, such as occupational records or community residence records, are generally used to identify groups for study. Risk: The probability that an event will occur, such as the probability that an individual will become ill or die within a stated period. Risk factor: An aspect of personal behavior or lifestyle, an environmental exposure, or an inborn or inherited characteristic that is known from epidemiologic evidence to be associated with adverse health effects.
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Sample size: The number of people selected (sampled) from a population to be the subjects of an epidemiologic study. Scoping study: Use of basic information about a site to provide bounding estimate for initial decisions on conducting an epidemiologic investigation. Security information: Information protected from public disclosure for reasons of national security, such as information about the design of nuclear weapons. Selection bias: Error that arises from systematic differences in characteristics between those who have been exposed to different amounts of a substance (in a cohort study), or between those who have and have not developed the disease of interest (in a case-control study). For example, selection bias would exist in a case-control study of radiation and lung cancer that did not account for persons in the case group who tended to smoke more cigarettes than did the controls. Sensitivity analysis: IEevaluation of the extent to which changes in the values of independent variables (or model parameters) of an equation (or mathematical model) bring about changes in the model result. Within the context of an uncertainty analysis, it is the evaluation of the extent to which uncertainty in the parameters (and in the functional relationships) in a mathematical model contributes to the overall uncertainty in the model result. By identifying the terms that dominate the overall uncertainty in the model result, a sensitivity analysis is an important tool for guiding research efforts. Sievert (Sv): The SI unit of dose equivalence equal to the dose in grays multiplied by the quality factor of the radiation. Solid-state dosimetry: Two methods available for the measurement of integrated dose in natural materials. They are thermoluminescence and electron paramagnetic resonance (EPR); the former is used with ceramic materials and quartz and the latter with tooth enamel. Approximate minimum detectable absorbed dose levels are 10 mGy (1 rad) and 100 mGy (10 rad) for thermoluminescence and EPR, respectively. Source term: The amount of radionuclides or chemicals released from a site to the environment over a specific period for use in dose reconstruction. Statistical power: See power. Statistical significance: A finding that, according to specific assumptions and based on mathematical probability, is not likely to have been the result of chance. In epidemiology for example, significance testing is a measure of whether a difference observed between the exposed and nonexposed groups in a study is real or merely a random variation. The probability of an observed difference being the
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result of chance can be expressed as a p-value. Stem cell: A cell that can differentiate into any one of several types. Susceptibility: The sensitivity of different people to the genotoxic effects of ionizing radiation, provided by different amounts of DNA repair capacity or different metabolic levels of biochemicals that prevent radiation genotoxicity. Thermoluminescence: One of two principal methods of solid-state dosimetry for the measurement of integrated dose in natural materials. Time dependence of dose: Dependence of the frequency of stochastic effects of radiation from dose rate and latent period make it necessary to take into account time-dependence of all kinds of doses delivered to the whole body or organs. In analyses of epidemiologic data, time-dependence of dose has to be taken into account for effects specific to different age and sex groups. Transfer factors from environmental data to dose: External dose for different groups of the population can be evaluated from dose rate measurements in open areas or from radioactive contamination as determined by spectrometric methods or by calculation. Internal dose from inhalation and ingestion can be evaluated from radionuclide concentration in air and in food products. Transuranic: An element with an atomic number greater than that of uranium (92). Uncertainty analysis: Quantification of the extent of uncertainty in the model result that is due to all conceivable sources. Most commonly, uncertainty analysis involves the probabilistic propagation of uncertainty in the parameters and in the functional terms of a model to provide a probabilistic statement for the model result from which a confidence interval can be obtained for decision-making. This confidence interval is most properly referred to as a "subjective confidence interval" or "credibility interval" given that judgment must be used to quantify the present state of knowledge about components of the model using incomplete or partially relevant data sets. Vadose zone: The unsaturated (shallow) soil layer that constitutes the region above the level of the permanent groundwater. Validity: The absence of systematic error or bias in, for example, a set of measurements. In epidemiology, validity also can refer to the degree to which study results are extrapolated to populations other than those in the study sample.
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