Any discipline has its own special terms and terminology. Epidemiology and the study of electric and magnetic fields are no exception. A few often-used terms which are employed throughout this report have been included to assist the reader. For additional information or further explanation of words or terms, please refer to many of the resources identified in Section 8 of this document.
DELTA-CONFIGURATION: Any triangular arrangement of the three-phase conductors of a line, as opposed to horizontal or vertical arrangements. It should be noted that not all delta variations are equal in their ability to reduce magnetic fields, but generally offer reductions as compared to horizontal or vertical configurations.
META-ANALYSIS: Meta-analysis is a way to combine the results of several epidemiologic studies. This technique is usually applied in epidemiology to increase statistical power (ability to detect an actual effect or difference) by increasing the sample size; or to improve estimates of the size of the effect. Findings of the meta-analysis are based on data from the primary studies and the extent to which these studies failed to take into consideration confounding factors would be reflected in the meta-analysis. It is believed that it is easier to publish studies based on "significant results" than studies with negative findings. The results of the analysis could be confounded, therefore, by a publication bias.
MISCLASSIFICATION BIAS: Epidemiology is not an exact science, and errors may occur in classifying individuals' exposure status or disease status. Classification may be from questionnaire data, estimated data or incomplete information. Misclassification bias can result in making an effect appear larger or smaller than it really is.
RELATIVE RISK: The term relative risk (RR) is used in epidemiologic studies to quantitatively characterize the risk of disease or death in a population exposed compared to a population unexposed. In EMF studies, because it is difficult to identify a truly "unexposed" population, researchers must compare groups who are "less exposed" to those who are "more exposed." When a study reports that "for children exposed to 3 mG or greater, the relative risk of leukemia is 2.5," it means that for children whose exposure experience is on average 3.0 mG or greater, their risk of contracting leukemia is 2.5 times greater than children who were not exposed to those fields.
ODDS RATIO: The odds ratio is an estimate of the relative risk calculated in case-control studies. It is the odds that a patient was exposed to the risk factor divided by the odds that a control was exposed.
STANDARDIZED MORTALITY RATIO: The standardized mortality ratio (SMR) is an indirect method of adjusting a rate. It is defined as the number of observed deaths (in the cohort) divided by the number of expected deaths. The expected number of deaths in the reference population by age group is applied to the number of persons in each age group in the study population to obtain the expected number of deaths in this population.
STATISTICAL SIGNIFICANCE: Statistical significance is generally interpreted as a result that would occur by chance less than 1 time in 20, with a Pvalue of less than or equal to 0.05. Statistical significance means that the finding is unlikely to be the result of chance. Confidence Intervals show the precision with which the relative risk or odds ratio was measured.