Instruments

Definition

A special feature in psychiatry is that diagnostic procedures for primary diagnosis mainly amount to the evaluation of questionnaires. In contrast to infectious diseases, for example, clinical-psychological test procedures primarily use validated forms to record the experience and behavior of patients.

Psychiatric instruments are tools used to assess mental health conditions, symptoms, and functioning in a standardized way. Each instrument typically has a title and a clear purpose, such as screening for a disorder, diagnosing a condition, or tracking symptom severity. For example, the Patient Health Questionnaire-9 (PHQ-9) is used to measure the severity of depression.

These instruments are usually divided into domains or areas they assess, like mood, energy levels, cognitive function, or sleep problems. For instance, a depression instrument may focus on areas like sadness, fatigue, and changes in appetite.

To assess these domains, the instrument includes a series of items — these are the individual questions or statements presented to the person being assessed. Items can be framed as questions, such as, “How often have you felt down or hopeless in the last two weeks?” or as statements like, “I feel nervous most of the time.”

Fig. First Item of PHQ-9 German Modification (Source: Kassenärztliche Bundesvereinigung)

Respondents answer these items using a specific response format, which is often a Likert scale. A Likert scale asks people to rate their experiences or symptoms on a range, such as 0 = “Not at all” to 3 = “Nearly every day.” Some instruments use simpler response formats, like Yes/No answers, or more detailed tools like visual analog scales, where someone marks their response along a line.

Each response is then converted into a numerical value as part of the scoring system. The scores are summed up to give a total score, which is interpreted based on defined ranges or cut-off values. For example, on the PHQ-9, a score between 0–4 indicates minimal depression, while a score between 10–14 suggests moderate depression.

Fig. Evaluation of PHQ-9 German Modification (Source: Kassenärztliche Bundesvereinigung)

The results of these instruments help clinicians make decisions, monitor progress over time, or determine eligibility for treatment studies. To ensure that the instrument is accurate and reliable, it undergoes testing for psychometric properties like reliability (whether it produces consistent results) and validity (whether it measures what it is supposed to measure).

Psychiatric instruments can be administered in several ways: people can complete them themselves (self-report), clinicians can guide the assessment (clinician-reported), or they can be completed by third parties which often happens with children and adolescents. To ensure accuracy across different populations, these tools may also need to be adapted for different cultures and languages.

In clinical and research settings, psychiatric instruments are used to screen for disorders, diagnose conditions based on criteria like ICD-11, measure treatment outcomes, and track changes in symptoms over time.