Outlier

{
  "id": "MLC-T-ENV-019957",
  "term": "Outlier",
  "field": "Environment",
  "definition": "1. Instances that are aberrant or do not fit with other instances: instances that, compared to other members of a population, are at the extremes on relevant dimensions.\n\n2. An extreme observation that is shown to have a low probability of belonging to a specified data population.\n\n3. Observations whose value is so extreme that they appear not to be consistent with the rest of the dataset. In a process monitor, outliers indicate that assignable or special causes are present. The deletion of a particular outlier from a data analysis is easiest to justify when such an unusual cause has been identified.\n\n4. An observation that is shown to have a low probability of belonging to a specified data population; any item rejected by the sampler, analyst, or data reviewer, usually accompanied by an attendant explanation. {ORD} {OW/EAD} {OPP} {OW/TSC} {OAR/OAQPS} {OECA} {ORCR}\n\n5. Observations whose value is so extreme that they appear not to be consistent with the rest of the dataset. In a process monitor, outliers indicate that assignable or special causes are present. The deletion of a particular outlier from a data analysis is easiest to justify when such an unusual cause has been identified. (NIST/SEMATECH 2005b)\n\n6. An outlier is an observation in a data set that is far removed in value from the others in the data set. It is an unusually large or an unusually small value compared to the others. An outlier might be the result of an error in measurement, in which case it will distort the interpretation of the data, having undue influence on many summary statistics, for example, the mean. If an outlier is a genuine result, it is important because it might indicate an extreme of behavior of the process under study. For this reason, all outliers must be examined carefully before embarking on any formal analysis. Outliers should not routinely be removed without further justification. (STEPS 1997)\n\n7. An observation that is shown to have a low probability of belonging to a specified data population; any item rejected by the sampler, analyst, or data reviewer, usually accompanied by an attendant explanation. (ORD)\n\n8. Data points well outside the range of others. [Choosing and Using Statistics: A Biologist's Guide]",
  "subject": "Policy and guidance",
  "references": [
    "Program Evaluation Glossary",
    "Guidance for Quality Assurance Project Plans",
    "NIST/SEMATECH 2005b",
    "Forum on Environmental Measurements (FEM) Glossary",
    "Thesaurus of Terms Used in Microbial Risk Assessment",
    "Environmental Sampling and Analytical Methods (ESAM) Program Glossary"
  ],
  "url": "https://mlchart.com/terminology/environment/outlier/"
}