Through the administration of a psychodiagnostic instrument a person who is being examined in a standardised way has the opportunity to express themselves, either directly or indirectly. Such a person is referred to in the profession as a “client”. The term covers people who can be assessed, such as pupils, applicants and patients. “Psychodiagnostic instruments” means instruments for determining someone’s characteristics with a view to making determinations about that person, in the context of advice to that person themselves, or to others about them, in the framework of treatment, development, placement, or selection.2 This psychodiagnostic context is at the heart of the AST-NIP. Nevertheless, scientific and professional requirements should also be set for the use of instruments and for users in other contexts.


Scientific research has shown that, when it comes to making psychological determinations about a person or group of persons, the use of psychodiagnostic instruments has important advantages over unwarranted judgments prompted by individual experience, intuition, feelings, sympathy, or empathy (see boxes 1 and 2). The results yielded by using psychodiagnostic instruments are often more reliable, more valid, more easily reproducible and more objective than those produced by an approach that emphasises unwarranted judgments. Moreover, the case can be made that psychodiagnostic instruments can be used more efficiently. In addition, these instruments ideally have norms, so that a client can be compared with people who are similar in terms of relevant characteristics.

The data obtained through the use of psychodiagnostic instruments is often the basis for taking important decisions about the person examined.

In order to ensure that no harm is done to the person who has been examined, data about a client must be obtained, used and transferred in a responsible manner. Two problems may come up when psychodiagnostic instruments are used:

  1. The instruments may not satisfy the necessary criteria, including scientific criteria.
  2. Psychodiagnostic instruments are used inappropriately.

In both cases, the results of an assessment will impact the possibilities offered by an assessment where psychodiagnostic instruments are used. The scientific and other criteria that psychodiagnostic instruments must meet are referred to in the AST-NIP. These criteria are also covered in the publications of the COTAN, such as the Committee´s system for assessing the quality of tests (Evers, Lucassen, Meijer, & Sijtsma, 2009).

The conditions for choosing the right test and the proper use of tests are also discussed in the AST-NIP. It is essential that a psychodiagnostic instrument be used for the right purpose and in the right way. If it is used improperly, a psychodiagnostic instrument can actually cause harm, with the result that the use of tests leads to pseudoscience and the deception of the client and the principal. In addition, one cannot blindly trust psychodiagnostic instruments. Diagnostics always involves more than just the use of tests. Psychodiagnostic instruments are thus tools for scientifically trained psychologists who are aware of both their advantages and limitations.

Please note that that the use of psychodiagnostic instruments is not equivalent to psychodiagnostic assessment. The “proper application of a psychodiagnostic instrument” indicates that the use of tests is part of a psychodiagnostic process and not a stand-alone activity. A psychologist should always clarify what the relationship is between the psychodiagnostic instrument that is used and the question that has been posed, as well as that between the test results and the findings that they3 come to on the basis of these. In addition, these results should always apply to the client.

The proper choice and use of psychodiagnostic instruments are primarily the responsibility of the psychologist. Guidance can be given on the responsible choice and use of psychodiagnostic instruments by formulating a standard for these. The professional use of tests also entails that the standard, too, actually serves to offer guidance. On the other hand, professionalism also entails that there can be deviations from the standard. If there is a wish to deviate from the standard, it is recommended that professional colleagues discuss this among themselves in advance and place what they have discussed in the file. The AST-NIP will offer more details on the conditions under which the use of psychodiagnostic instruments adds value in the context of psychodiagnostics, psychological treatments, and/or the evaluation of these latter.

2 For stylistic reasons, “psychodiagnostic instrument” and “test” are used interchangeably in the AST-NIP, and “test” can thus also refer to a questionnaire, an observation scale, or a standardised interview, for instance.

3 By contrast with the treatment of personal pronouns and possessive adjectives in the original Dutch version of the AST-NIP, this translation makes use of an option available in English: the gender-neutral, nominally plural form of personal pronouns and possessive adjectives for subjects in the singular, unless of course the gender of the subject is specified (“their son…he/him/his”). Thus, as a general matter, that gives, “the psychologist…they/them/their”, and so on.