An essential factor that plays a role in selecting diagnostic instruments is the treatment of the candidate before, during and after the test. Best practice entails:

Transparency
A good diagnostic instrument should provide an appropriate degree of transparency. This contains that informative and understandable instructions explain the test background and the administration process (time limits etc.) before the test starts and that practice items are available to explain the principle of the test or questionnaire. Additionally, in case of online-administrations, a trained test administrator should explain the system.

Feedback
It should be ensured, that each candidate who worked through a specific instrument, receives appropriate feedback about his/her performance (ability tests) or results (questionnaires) after having finished. At least, a short written feedback report (preferably narrative) should be provided. In best case, personal feedback should be provided by a trained person and by means of a detailed feedback report.

Equal opportunities
Furthermore, it is important in terms of fairness that the resulting test scores do not cause a systematic discrimination of specific persons because of their membership to ethnic, socio-cultural or gender-specific groups. For the purpose of accessibility all persons should have the same possibilities to attend to diagnostic instruments. That means, amongst other things, that also people with disabilities get the possibility, adequate to their abilities, to attend to diagnostic instruments, possibly by means of input assistance.