When large numbers of tests are performed, some produce false results of this type hence 5% of randomly chosen hypotheses might be (erroneously) reported to be statistically significant at the 5% significance level, 1% might be (erroneously) reported to be statistically significant at the 1% significance level, and so on, by chance alone. This level of risk is called the significance. The process of data dredging involves testing multiple hypotheses using a single data set by exhaustively searching-perhaps for combinations of variables that might show a correlation, and perhaps for groups of cases or observations that show differences in their mean or in their breakdown by some other variable.Ĭonventional tests of statistical significance are based on the probability that a particular result would arise if chance alone were at work, and necessarily accept some risk of mistaken conclusions of a certain type (mistaken rejections of the null hypothesis). This is done by performing many statistical tests on the data and only reporting those that come back with significant results.
JSTOR ( October 2016) ( Learn how and when to remove this template message)Ī humorous example of a result produced by data dredging, showing a coincidental correlation between the number of letters in Scripps National Spelling Bee's winning word and the number of people in the United States killed by venomous spiders.ĭata dredging (also known as data snooping or p-hacking) is the misuse of data analysis to find patterns in data that can be presented as statistically significant, thus dramatically increasing and understating the risk of false positives. Unsourced material may be challenged and removed. 
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Many distorted fragments of meteoritic iron are later dredged up from the area where the wreckage fell.This article needs additional citations for verification. It must have been seeing her reading Tennyson that had dredged up an old forgotten quotation. The scheme involves dredging the main channel of the Medway estuary to provide a storage base for import-export cargoes. Others specialize in dredging operations required for bridges and dams or for harbors. Fearing more floods, the state had the river dredged. 2 DF to cover food lightly with flour, sugar etc → dredge something ↔ up → See Verb table Examples from the Corpus dredge From Longman Dictionary of Contemporary English Related topics: Water, Civil, Food dredge dredge / dredʒ / verb 1 TTW TEC to remove mud or sand from the bottom of a river, harbour etc, or to search for something by doing this They dredged for oysters.
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