Statistical Significance 1
Statistical Significance 1 : (a) The probability of obtaining a result as extreme or more extreme as that observed even if the null hypothesis is true. [FACS, 2000: Epidemiology for Journalists]; (b) The probability that a result likely to be due to chance alone. By convention, a difference between two groups is usually considered statistically significant if chance could explain it only 5% of the time or less. Study design considerations may influence the a priori choice of a different statistical significance level. [IRIS, 1999: Glossary of IRIS Terms]; (c) Statistical methods allow an estimate to be made of the probability of the observed or greater degree of association between independent and dependent variables under the null hypothesis. From this estimate, in a sample of given size, the statistical "significance" of a result can be stated. Usually the level of statistical significance is stated by the P value. [Last, 1983: A Dictionary of Epidemiology]; (d) the probability that an event or difference occurred as the result of the intervention (vaccine) rather than by chance alone. This probability is determined by using statistical tests to evaluate collected data. Guidelines for defining significance are chosen before data collection begins. [NIAID, 1997: HIV Vaccine Glossary]; (e) The statistical significance determined by using appropriate standard techniques of statistical analysis with results interpreted at the stated confidence level and based on data relating species which are present in sufficient numbers at control areas to permit a valid statistical comparison with the areas being tested. [SRA, 1999: Glossary of Risk Analysis Terms] [USDOE, 2000: RAIS Glossary]; (f) An inference that the probability is low that the observed difference in quantities being measured could be due to variability in the data rather than an actual difference in the quantities themselves. The inference that an observed difference is statistically significant is typically based on a test to reject one hypothesis and accept another. [USEPA, 1992: GL for Exposure Assessment]
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