Trust metric

Trust metrics may be abstracted in a manner that can be implemented on computers, making them of interest for the study and engineering of virtual communities, such as Friendster and LiveJournal.

Trust escapes a simple measurement because its meaning is too subjective for universally reliable metrics, and the fact that it is a mental process, unavailable to instruments.

Slashdot introduced its notion of karma, earned for activities perceived to promote group effectiveness, an approach that has been very influential in later virtual communities.

Those methods combine theoretical background (determining what it is that they measure) with defined set of questions and statistical processing of results.

The actual value (level of trust and/or trustworthiness) is assessed from the difference between observed and hypothetical behaviors i.e. those that would have been anticipated in the absence of cooperation.

Specifically the Prisoners Dilemma[17] are popularly used to link trust with economic utility and demonstrate the rationality behind reciprocity.

[25] Some metrics use ordered set of values without attempting to convert them to any particular numerical range (e.g.[26] See[27] for a detailed overview).

Subjective logic is an example of computational trust where uncertainty is inherently embedded in the calculation process and is visible at the output.

It is not the only one, it is e.g. possible to use a similar quadruplet (trust, distrust, unknown, ignorance) to express the value of confidence,[32] as long as the appropriate operations are defined.

[34] Both share a common representation, which is equivalent to subjective opinions, but based on three independent parameters named 'average rating', 'certainty', and 'initial expectation'.

Fuzzy systems,[35] as trust metrics can link natural language expressions with a meaningful numerical analysis.

Application of fuzzy logic to trust has been studied in the context of peer-to-peer networks[36] to improve peer rating.

Also for grid computing[37] it has been demonstrated that fuzzy logic allows to solve security issues in reliable and efficient manner.

However, the attempt to attribute exact formal semantics to transitivity reveals problems, related to the notion of a trust scope or context.

Each interpretations leads to different results, depending on the assumptions for trust fusion in the particular situatation to be modelled.

The free software developer resource Advogato is based on a novel approach to attack-resistant trust metrics of Raph Levien.

Levien observed that Google's PageRank algorithm can be understood to be an attack resistant trust metric rather similar to that behind Advogato.