to a set of questions or statements and responses are e.g. structured according to a Likert scale. Differentiating factors are the underlying theoretical background and contextual relevance. One of the earliest surveys are McCroskey's scales that have been used to determine authoritativeness (competence) and character (trustworthiness) of speakers. Rempel's trust scale and Rotter's scale are quite popular in determining the level of interpersonal trust in different settings. The Organizational Trust Inventory (OTI) is an example of an exhaustive, theory-driven survey that can be used to determine the level of trust within the organisation. For a particular research area a more specific survey can be developed. For example, the interdisciplinary model of trust, has been verified using a survey while uses a survey to establish the relationship between design elements of the web site and perceived trustworthiness of it. Games Another empirical method to measure trust is to engage participants in experiments, treating the outcome of such experiments as estimates of trust. Several games and game-like scenarios have been tried, some of which estimate trust or confidence in monetary terms (see for an interesting overview). Games of trust are designed in a way that their Nash equilibrium differ from Pareto optimum so that no player alone can maximize their own utility by altering his selfish strategy without cooperation, while cooperating partners can benefit. Trust can be therefore estimated on the basis of monetary gain attributable to cooperation. The original 'game of trust' has been described in as an abstracted investment game between an investor and his broker. The game can be played once or several times, between randomly chosen players or in pairs that know each other, yielding different results. Several variants of the game exist, focusing on different aspects of trust as the observable behaviour. For example, rules of the game can be reversed into what can be called a game of distrust, declaratory phase can be introduced or rules can be presented in a variety of ways, altering the perception of participants. Other interesting games are e.g. binary-choice trust games, the gift-exchange game, cooperative trust games, and various other forms of social games. Specifically the Prisoners Dilemma are popularly used to link trust with economic utility and demonstrate the rationality behind reciprocity. For multi-player games, different forms of close market simulations exist. Formal metrics Formal metrics focus on facilitating trust modelling, specifically for large scale models that represent trust