PHQ-9 and the Beck Depression Inventory-II are two different questionnaires for assessing the severity of depressive symptoms. Their structure, administration and scoring rules differ, so their scores cannot be compared directly. A test result is not a diagnosis. Diagnosis requires consultation with a doctor.
What PHQ-9 assesses
PHQ-9 consists of nine items about symptoms during the previous two weeks. It is a brief self-report questionnaire designed to identify diagnostic features of a depressive episode. The result helps describe symptom severity and monitor change. To establish a diagnosis, it is considered together with how symptoms affect daily life, the person’s history and any risks.
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A high score does not prove that a depressive disorder is present, and a low score does not rule out another problem. Physical illness, sleep disturbance, anxiety, stressful events and other circumstances can affect responses.
What the Beck Depression Inventory-II assesses
BDI-II is a 21-item self-report questionnaire used to assess the intensity of depressive symptoms. It covers cognitive, emotional and physical features and has its own administration and interpretation rules. Official materials and normative data belong to the rights holder, Pearson.
A qualified professional may use BDI-II during an assessment. An unofficial online version without a clear source, version or scoring rules is not suitable for medical conclusions.
Why the two scores may differ
The questionnaires contain different numbers of items, describe symptoms differently and use their own score ranges. They may reflect cognitive and physical symptoms differently. A PHQ-9 score therefore cannot be converted into a BDI-II score with a simple formula.
Responses also depend on how the person felt during the specified period, how they understood the questions and how they judged the frequency or intensity of symptoms.
Which questionnaire should I choose?
For an initial self-check, a brief validated instrument with transparent rules, such as PHQ-9, can be convenient. During a professional assessment, the clinician selects a method according to the purpose, age, condition and setting.
There is no need to complete many questionnaires in search of the “right” answer. It is more useful to save one result, note the symptoms causing the most difficulty and discuss them during a consultation.
What to do after receiving a PHQ-9 result
Consider the duration of symptoms and their effect on sleep, work, study, relationships and self-care as well as the total score. If the condition persists, worsens or interferes with daily life, seek a professional assessment.
Any response about thoughts of death or self-harm requires prompt, separate assessment regardless of the total score. If there is immediate danger, do not remain alone and contact a psychiatrist or emergency service now.
Common questions
Neither test is universally more accurate in every situation. The choice depends on the purpose and setting, and the result requires clinical context.
No. They should not be compared directly because the scales have different structures and interpretation rules.
It means that the reported symptoms are pronounced and deserve attention. A professional establishes a diagnosis after a broader assessment.