Statistical Significance

{
  "id": "MLC-T-ENV-026725",
  "term": "Statistical Significance",
  "field": "Environment",
  "definition": "1. The probability that a result is not 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 level of statistical significance.\n\n2. The degree to which a value is greater or smaller than would be expected by chance. Typically, a relationship is considered statistically significant when the probability of obtaining that result by chance is less than 5% if there were, in fact, no relationship in the population.\n\n3. 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.\n\n4. Conclusion that an intervention has a true effect, based upon observed differences in outcomes between the treatment and control groups that are sufficiently large so that these differences are unlikely to have occurred due to chance, as determined by a statistical test. Statistical significance indicates the probability that the observed difference was due to chance if the null hypothesis is true; it does not provide information about the magnitude of a treatment effect.\n\n5. 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. 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 level of statistical significance. See Guidelines for Exposure Assessment (EPA, 1992) and IRIS Glossary (2016).\n\n6. Statistical significance determined by using appropriate standard techniques of multivariate analysis with results interpreted at the 95 percent 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.",
  "subject": "Health and safety",
  "references": [
    "Integrated Risk Information System (IRIS) Glossary; EPA 2003",
    "Program Evaluation Glossary",
    "EPA 1992",
    "NLM/NICHSR 2004",
    "Health Effects Notebook Glossary",
    "40 CFR 228.2 (CCFR 2013)"
  ],
  "url": "https://mlchart.com/terminology/environment/statistical-significance/"
}