Delphi can be labeled an expert method. In this aspect the Delphi method differs from standard survey methods, where statistical and probability models are used. In statistical sampling, the respondents must represent the target population in the real world. Sample data consists of observed relative frequencies of individuals exhibiting the properties of interest. Statistical models are models of population. A sample is taken from the population so that the occurrence of the feature in the population can be deduced from the sample (in relation to its frequency in the sample) using probabilistic reasoning, within a margin of error. This probabilistic
reasoning is done using a probability model.(Miles and Huberman 1994.) In a Delphi study, experts are selected from among the experts of a field of
study, and the aim is to cover all the relevant aspects of the study subject (e.g. Okoli and Pawlowski 2004). Good coverage of views rather than representativeness is called for (Kuusi 1999). The experts are then brought into interaction with the topic and with each other in a way that emphasizes the rationale of the arguments instead of the position or authority of the expert in question. In Delphi studies on technology foresight, large group of experts are usually favored, while, in social issues for example, the number of experts is relatively small. (Gordon 2011.)
The appeal of Delphi as a method is based on its characterization as an expert method. Thus, one of the most critical phases of a Delphi study, according to many Delphi practitioners, is the selection of experts. The Delphi method is well
suited for setting up a communication structure among members who possess the same general core of knowledge and who are already well informed. (Gordon 2011; Kuusi 1999; Laakso, Rubin, and Linturi 2012; Linstone and Turoff 1975b.) The most knowledgeable people in their field of specialization are often also ahead of others in their ideas about the future because of their exceptional understanding (Kuusi 1999). According to Kuusi (1999), an expert fit for a Delphi study should be:
1. At the highest level of his/her field of knowledge/science 2. Interested in a wide range of knowledge (around it)
3. Able to trace connections between national and international, present and future development
4. Able to regard problems from an unconventional point of view as well 5. Interested in doing something new.
The competence of an expert, expertise, may be determined both cognitively and socially. Expertise as a cognitive property refers to the acquired knowledge and skills possessed by an expert, whereas expertise as a social property refers to the possession of expert status in the eyes of others (Varho and Huutoniemi 2014). Varho and Huutoniemi (2014) further explore expertise as follows:
“From a cognitive perspective, expertise is the possession of substantive knowledge of a domain of activity, including both propositional knowledge and tacit knowledge, and it can be acquired e.g. through education, research, experience, occupation, or any other form of cognitive refinement. Even though the social status of an expert is often gained through demonstrated competence in a given area, the acquisition of expert status is a different social process than the acquisition of cognitive expertise.”
Typically social status comes through formal degrees, higher professions, and leading organizational positions that give a person the status of an expert in a particular domain (Saaristo 2000).
It is good to have diversity among experts in Delphi: it generates a variety of opinions, which can then be taken into account by all of the experts (Hussler, Muller, and Rondé 2011). This means that successful realization of Delphi requires the design of an expert group structure that allows many knowledgeable individuals from different disciplines or specialties, who have a different working background and experience, and who contribute information or judgments on the problem area which is broader in scope than the knowledge that any single individual can possess. (Gordon 2011; Kuusi 1999; Laakso, Rubin, and Linturi 2012; Linstone and Turoff 1975b.)
In order to help cover all the desired areas of both cognitive and social expertise when selecting the experts for a Delphi study, one possibility is to use an expertise matrix, recently developed and discussed in Finland among Delphi practitioners, especially by Osmo Kuusi (Kuusi, Ryynänen, Kinnunen, Myllykangas, and Lammintakanen 2006; Kuusi 2013). The matrix is two- dimensional: one dimension describes the desired interest groups of the experts, and the other dimension describes the desired competence areas which the experts should represent (Table 1).
Table 1 The principle of competence a area-interest group matrix
Cognitive expertise Social expertise
Interest group 1 Interest group 2 Interest group n
Competence area 1 Competence area 2 Competence area n
When using the matrix, the Delphi facilitator (researcher) should consider the kinds of organizations relevant to the topic and the research questions of the study. There may be different basic assumptions on the topic, e.g. the public sector may have different views compared to the private sector; these would represent the interest groups. On the other hand, again based on the topic and the research questions, the facilitator should consider which kind of cognitive competences should be represented in the study; e.g. engineering, marketing, management, etc. Finally, by placing selected experts into the matrix the facilitator may ensure that all the desired aspects of expertise are covered. (Kuusi 2013.) For example, in their work on future food consumption, Vinnari and Tapio (2008) defined researchers, non-governmental organizations, politicians, and companies as the form of social expertise and, respectively, politics, economics, social and culture, technology, and environment and ethics as the cognitive competence areas.