Why use it

The MDI uniquely combines severity measurement with the ability to generate ICD-10 and DSM-IV diagnostic categories — making it suitable both for initial screening and for monitoring treatment response. It provides a dimensional severity score alongside a categorical diagnostic classification, which is useful in clinical practice where both are needed. The tool has good sensitivity and specificity for moderate-to-severe depression and tracks treatment response over time.

About

The Major Depression Index (MDI) is a 10-item self-report questionnaire developed by Bech and colleagues and published in Acta Psychiatrica Scandinavica in 2001. The MDI was designed to serve a dual purpose: (1) as a screening and severity rating scale for major depressive disorder (MDD) and (2) as a diagnostic instrument capable of generating a DSM-IV or ICD-10 diagnosis of depression based on item endorsement patterns. Each item covers one of the core symptom domains of depression over the past 2 weeks, rated on a 6-point Likert scale (0 = "At no time" to 5 = "All the time"). Two items (low mood and loss of interest) have two sub-items each, and the higher of the two sub-item scores is used in the total. The total MDI score ranges from 0 to 50. It is widely used in Scandinavian and European primary care and psychiatric settings and has been validated across many countries and clinical populations.

When to use

Initial screening for depressive disorder in primary care, outpatient psychiatry, or general medical settings
Establishing a diagnostic classification (mild, moderate, or severe depression per ICD-10/DSM-IV) using symptom pattern
Monitoring treatment response and remission in patients with known MDD
Population-based mental health screening studies
When a longer severity rating (vs. PHQ-2 or GAD-7) with diagnostic capability is needed
Assessment at first psychiatric contact, then at follow-up visits (typically every 4–8 weeks during acute treatment)

Formula

MDI Items (scored 0–5 each): 0 = At no time 1 = Some of the time 2 = Less than half the time 3 = More than half the time 4 = Most of the time 5 = All the time Items: 1. Low mood (felt low, sad, desperate, hopeless) 2. Loss of interest and pleasure 3. Reduced energy, tiredness 4. Loss of confidence 5. Guilty feelings, self-reproach 6. Recurrent thoughts of death or suicide 7. Reduced concentration or difficulty making decisions 8. Psychomotor agitation or retardation — HIGHER of: 8a. Feeling restless and agitated 8b. Feeling slow and sluggish 9. Sleep problems — HIGHER of: 9a. Sleep disturbance (difficulty sleeping) 9b. Sleeping too much 10. Appetite — HIGHER of: 10a. Reduced appetite 10b. Increased appetite Total: 0–50 0–20: No/minimal depression 21–25: Mild depression 26–30: Moderate depression 31–50: Severe depression

Pearls & pitfalls

Items 8a and 8b (reduced appetite/increased appetite) and items 10a and 10b (reduced sleep/increased sleep) each use the HIGHER of the two sub-item scores in total calculation — not the sum.
For ICD-10 diagnosis of major depression, the core symptoms are: low mood, loss of interest, and reduced energy. At least 2 of these 3 must be endorsed (score ≥2) for mild depression.
DSM-IV diagnostic criteria require at least 5 of 9 symptom criteria present for ≥2 weeks, with at least 1 being depressed mood or anhedonia.
The MDI total score alone does not generate the ICD-10/DSM diagnosis — pattern of item endorsement must be evaluated (not automated in simple score sum).
MDI ≥26 has shown good sensitivity (~80%) and specificity (~86%) for ICD-10 moderate or severe depression in validation studies.
The MDI was validated in a Danish primary care setting and showed excellent psychometric properties: Cronbach alpha = 0.87, good convergent validity with Hamilton Depression Rating Scale (HDRS) and Beck Depression Inventory (BDI).
The MDI is available in over 20 languages — always use a validated translation for non-English speaking patients.
Response in treatment monitoring is defined as ≥50% reduction in MDI score from baseline. Remission is defined as MDI ≤12.
The MDI should NOT be used as a substitute for a full psychiatric interview in patients with active suicidal ideation or other safety concerns.

Next steps

MDI 0–20 (No/Minimal Depression): Symptoms below threshold. No further depressive treatment indicated. Address other contributing factors. MDI 21–25 (Mild Depression): Mild depressive episode. Consider watchful waiting, supportive counseling, and psychoeducation. Reassess in 2–4 weeks. MDI 26–30 (Moderate Depression): Moderate depressive episode. Psychotherapy (CBT, IPT) recommended. Consider antidepressant therapy. Refer to specialist if no improvement in 4–6 weeks. MDI 31–50 (Severe Depression): Severe depressive episode. Antidepressant therapy indicated. Specialist psychiatric referral recommended. Assess for suicidality. Consider inpatient admission if safety concerns.

Evidence

Bech P et al. The Major Depression Inventory (MDI): a validation study. Acta Psychiatr Scand. 2001;104(3):214-219. PMID:11531652. Validated in Danish primary care (n=257). Sensitivity 86%, specificity 82% at cut-off ≥26 for ICD-10 major depression. Confirmatory validation in Olsen LR et al. Acta Psychiatr Scand. 2003;107(6):416-22. Cronbach alpha = 0.87. Also validated as diagnostic instrument using ICD-10 and DSM-IV criteria using item endorsement patterns.

References

Bech P et al. The Major Depression Inventory (MDI): a validation study in patients with major depression. Acta Psychiatr Scand. 2001;104(3):214-219. — link
Olsen LR et al. The internal and external validity of the Major Depression Inventory in measuring severity of depressive states. Psychol Med. 2003;33(2):351-356. — link
Cuijpers P et al. Screening for mood and anxiety disorders with the five-item, the three-item and the two-item Mental Health Inventory. Psychiatry Res. 2009;168(3):250-255. — link

Major Depression Index (MDI)

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