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Printed on 6/29/2026
For informational purposes only. This is not medical advice.
The Major Depression Inventory (MDI) is a self-report mood questionnaire developed by the WHO Collaborating Centre in Mental Health. It consists of 10 items rated from 0 (at no time) to 5 (all the time), covering the past 2 weeks. The MDI can be used as a diagnostic instrument (ICD-10 criteria) or as a severity measure (sum score 0–50). Severity: <20 no depression, 20–24 mild, 25–29 moderate, ≥30 severe. Unlike the BDI-II, the MDI is freely available and WHO-endorsed, making it widely used in research and primary care globally.
Formula: Sum of 10 items (each 0–5). For paired items (8a/8b, 10a/10b), use the higher score. Total: 0–50.
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The MDI asks patients to rate how often they have experienced each of 10 depression symptoms over the past 2 weeks. The 6-point response scale ranges from 5 (all the time) to 0 (at no time). Items cover the core DSM-IV and ICD-10 depression criteria: depressed mood, loss of interest and pleasure, loss of energy and vitality, loss of confidence and self-esteem, guilt and self-reproach, suicidal thoughts and acts, concentration difficulties, psychomotor agitation or retardation, sleep disturbance, and appetite changes. Two items (sleep changes and appetite changes) have paired sub-items — for these, the higher of the two sub-item scores is used.
The MDI can be used in two ways. First, as a continuous severity measure: sum all 10 item scores (using the higher sub-item score for paired items) to produce a total between 0 and 50. Second, as a diagnostic tool: apply the DSM-IV algorithm to identify whether the symptom pattern meets criteria for a major depressive episode. The diagnostic algorithm requires that specific core symptoms score 4 or above (present more than half the time) for 2 weeks. Both uses are valid, but the application must be specified when interpreting results.
Severity interpretation: 0-20 = no or minimal depression; 21-25 = mild depression; 26-30 = moderate depression; 31-50 = severe depression. DSM-IV diagnostic algorithm positive for major depressive episode requires: at least 2 of 3 core symptoms (depressed mood, loss of interest, loss of energy) scoring 4+, plus at least 4 additional symptoms scoring 4+, for at least 2 weeks. Clinical action should be guided by both the severity score and functional impairment.
Psychiatrists
The MDI's 0-50 continuous scale provides fine-grained tracking of depression severity response to antidepressant therapy or psychotherapy across treatment visits. Its ICD-10 alignment makes it preferred in European psychiatric practice.
European General Practitioners
The MDI is widely used in Scandinavian and broader European primary care for initial depression screening and treatment monitoring. Its free availability and WHO endorsement support integration into routine primary care workflows.
Clinical Researchers
The MDI has been used as a primary endpoint in depression intervention studies, particularly in European contexts. Its dual function as both severity measure and diagnostic classifier enables both continuous and categorical outcome analyses from the same instrument.
Psychopharmacologists
The MDI severity score tracks antidepressant response with greater granularity than binary remission criteria. A 50% reduction from baseline is a standard research response definition, and a score below 20 represents remission.
Epidemiologists
The MDI has been used in large-scale Danish and Nordic mental health population surveys and national registers. Its free availability and ICD-10 alignment made it the instrument of choice for Nordic epidemiological research on depression prevalence and burden.
The MDI is the standard depression measurement tool in Danish, Norwegian, and broader Scandinavian mental health systems, where ICD-10 rather than DSM-5 is the diagnostic standard. In the US, the PHQ-9 is far more commonly used in both primary care and research. Both tools have comparable validity for depression severity measurement, and the choice of instrument should be guided by local clinical context and whether ICD-10 or DSM-5 diagnostic criteria are used.
One of the MDI's most valuable features is that the same 10 items can be used both as a continuous severity measure (sum score 0-50) and as a diagnostic tool applying DSM-IV criteria for major depressive episode. This dual function means a single administration provides both quantitative severity data and a categorical diagnostic classification without requiring additional questionnaires. Specify the intended use (severity measurement vs diagnostic classification) before administration to ensure appropriate interpretation.
For the MDI's DSM-IV diagnostic algorithm, core and additional symptoms must score 4 or 5 (present more than half the time or all the time) to count toward criteria. Simply being present at any level (score 1-3) is insufficient for the diagnostic algorithm. This frequency threshold is a key distinction from the PHQ-9, which uses a different scoring approach. When using MDI diagnostically, always apply the frequency threshold rather than treating any non-zero score as criterion-positive.
For moderate to severe major depression (MDI 26+), first-line treatment is typically antidepressant pharmacotherapy (SSRIs or SNRIs) combined with psychotherapy. CBT (cognitive behavioral therapy) and IPT (interpersonal therapy) have the strongest evidence base for depression. Combined treatment is more effective than either alone for severe depression. For mild-moderate depression (MDI 21-25), psychotherapy alone may be offered as first-line treatment based on patient preference.
In MDI treatment monitoring, a 50% reduction from baseline severity score is the standard research definition of 'treatment response.' A score below 20 (no or minimal depression) represents clinical remission. When tracking antidepressant response, administer the MDI at baseline and at 4, 8, and 12 weeks. A persistent score above 25 after 8 weeks at therapeutic dose should prompt reassessment of diagnosis, dose, or regimen.
For patients with moderate to severe depression, the evidence clearly supports combining antidepressants with psychotherapy over either treatment alone. Meta-analyses show that combination therapy produces significantly higher response and remission rates and lower relapse rates. The MDI tracking this combined treatment should show more rapid and sustained score reduction than single-modality treatment. Consider referral to a psychologist for CBT or IPT alongside pharmacotherapy for all patients with MDI scores above 25.
The MDI was developed specifically to include all symptom criteria from both ICD-10 and DSM-IV major depression in a single self-report instrument. This makes it uniquely capable of supporting both diagnostic systems from the same administration — an advantage in research and in international settings where both coding systems are used. No other brief self-report depression measure simultaneously covers all criteria from both the ICD-10 and DSM-IV depressive episode definitions.
Unlike the BDI-II, which is copyrighted and requires commercial licensing, the MDI is available free of charge for non-commercial clinical and research use. This has made it widely adopted in public health systems, low-resource settings, and large population surveys where copyright licensing is a barrier. Permission for clinical use can be obtained from the copyright holders at the WHO Collaborating Centre in Mental Health, Copenhagen, Denmark.
MDI published by Bech et al. (Acta Psychiatr Scand 2001) from 171 psychiatric outpatients. C-statistic 0.87 for DSM-IV MDE. Internal consistency alpha 0.89. Validated against ICD-10 and DSM-IV criteria. MDI sensitivity for DSM-IV MDE: 90% at threshold 26. Widely used in Danish and Nordic mental health research. Compared to PHQ-9: Cuijpers et al. (J Affect Disord 2010) systematic review. Available free from copyright holders for non-commercial clinical use.
Your MDI score reflects the severity of depressive symptoms you have experienced over the past two weeks. A score below 20 suggests no or minimal depression. A score of 20 to 24 indicates mild depression, meaning you may be experiencing some low mood and reduced enjoyment but can still function in daily activities. A score of 25 to 29 indicates moderate depression, where symptoms are more pervasive and likely interfering with work, relationships, or daily routines. A score of 30 or above indicates severe depression, suggesting significant impairment that typically warrants prompt clinical attention.
The MDI can also be used diagnostically by mapping specific item responses to ICD-10 criteria for depressive episodes. For a diagnostic interpretation, at least two of the three core symptoms (depressed mood, loss of interest, fatigue) must score 4 or higher, along with additional qualifying symptoms. Your clinician can help determine whether your responses meet the threshold for a formal ICD-10 diagnosis of depression.
The MDI is appropriate for routine depression screening in primary care, mental health clinics, and research settings. It is particularly useful in international contexts because it is freely available and WHO-endorsed, eliminating licensing barriers. Clinicians may administer it at initial intake visits, during follow-up appointments to track treatment response, or as part of population health screening programs.
The MDI is also valuable when an ICD-10-aligned diagnostic assessment is preferred over a DSM-based tool. Because it can serve both as a continuous severity measure and as a diagnostic algorithm, it offers flexibility that some other depression instruments lack. It is suitable for adults in both clinical and community settings.
The MDI is a self-report instrument and depends on the respondent's insight, honesty, and literacy. Patients with severe depression, cognitive impairment, or psychotic features may underreport or have difficulty completing the questionnaire accurately. It does not replace a comprehensive clinical interview for diagnosing depression.
The MDI does not assess anxiety, bipolar features, or psychotic symptoms, which frequently co-occur with depression. A high MDI score should prompt further evaluation to rule out other psychiatric conditions. Additionally, somatic symptoms captured by the MDI (fatigue, sleep changes, appetite changes) can be caused by medical illnesses, potentially inflating scores in medically ill populations.
While the MDI has been validated in multiple languages and populations, cultural factors can influence how individuals interpret and report mood symptoms. Clinicians should consider the patient's cultural background when interpreting results.
For related assessments, see PHQ-9, PHQ-2 and BDI-II Score.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
April 21, 2026 · trust-baseline
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