The subadditivity effect is the tendency to judge

probability Probability is the branch of mathematics concerning numerical descriptions of how likely an Event (probability theory), event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and ...

of the whole to be less than the probabilities of the parts.

Example

For instance, subjects in one experiment judged the probability of death from cancer in the United States was 18%, the probability from heart attack was 22%, and the probability of death from "other

natural causes In many legal jurisdictions, the manner of death is a determination, typically made by the coroner, medical examiner, police, or similar officials, and recorded as a vital statistic. Within the United States and the United Kingdom, a disti ...

" was 33%. Other participants judged the probability of death from a natural cause was 58%. Natural causes are made up of precisely cancer, heart attack, and "other natural causes," however, the sum of the latter three probabilities was 73%, and not 58%. According to Tversky and Koehler (1994) this kind of result is observed consistently.

Explanations

In a 2012 article in ''

Psychological Bulletin The ''Psychological Bulletin'' is a monthly peer-reviewed academic journal that publishes evaluative and integrative research reviews and interpretations of issues in psychology, including both qualitative (narrative) and/or quantitative ( meta-ana ...

'' it is suggested the subadditivity effect can be explained by an

information-theoretic Information theory is the scientific study of the quantification, storage, and communication of information. The field was originally established by the works of Harry Nyquist and Ralph Hartley, in the 1920s, and Claude Shannon in the 1940s. ...

generative mechanism that assumes a noisy conversion of objective evidence (observation) into subjective estimates (judgment). This explanation is different than

support theory Support may refer to: Arts, entertainment, and media * Supporting character Business and finance * Support (technical analysis) * Child support * Customer support * Income Support Construction * Support (structure), or lateral support ...

, proposed as an explanation by Tversky and Koehler, which requires additional assumptions. Since mental noise is a sufficient explanation that is much simpler and straightforward than any explanation involving heuristics or behavior,

Occam's razor Occam's razor, Ockham's razor, or Ocham's razor ( la, novacula Occami), also known as the principle of parsimony or the law of parsimony ( la, lex parsimoniae), is the problem-solving principle that "entities should not be multiplied beyond neces ...

would argue in its favor as the underlying generative mechanism (it is the hypotheses which makes the fewest assumptions).

References

{{Reflist, refs= {{cite book, last1=Baron, first1=Jonathan, title=Thinking and Deciding, date=2009, publisher=Cambridge University Press, isbn=978-0521680431, edition=4 {{cite journal, last1=Tversky, first1=Amos, last2=Koehler, first2=Derek J., title=Support theory: A nonextensional representation of subjective probability., journal=Psychological Review, date=1994, volume=101, issue=4, pages=547–567, doi=10.1037/0033-295X.101.4.547, url=http://users.physics.harvard.edu/~wilson/freshman_seminar/Tversky/Tversky%20and%20Koehler%20-%20Support%20Theory%20-%20A%20Nonextensional%20Representation%20ofSubjection%20Probability%20-%201994%20-%20Psychological%20Review.pdf, url-status=bot: unknown, archiveurl=https://web.archive.org/web/20160506192515/http://users.physics.harvard.edu/~wilson/freshman_seminar/Tversky/Tversky%20and%20Koehler%20-%20Support%20Theory%20-%20A%20Nonextensional%20Representation%20ofSubjection%20Probability%20-%201994%20-%20Psychological%20Review.pdf, archivedate=2016-05-06 {{cite journal, last1=Hilbert, first1=Martin, title=Toward a synthesis of cognitive biases: How noisy information processing can bias human decision making, journal=Psychological Bulletin, date=2012, volume=138, issue=2, pages=211–237, doi=10.1037/a0025940, url=http://www.martinhilbert.net/HilbertPsychBull.pdf, pmid=22122235, url-status=bot: unknown, archiveurl=https://web.archive.org/web/20160304023236/http://www.martinhilbert.net/HilbertPsychBull.pdf, archivedate=2016-03-04, citeseerx=10.1.1.432.8763 Cognitive biases Error Barriers to critical thinking