The COVID-19 pandemic, armed conflicts, economic dislocations and other concerns have affected mental health around the globe. Clinical depression, which affects 300 million individuals worldwide, is projected to increase.

With findings that are significant for both clinicians and patients, a large international study has shown that the most commonly used clinical measurement tool for depression, the PHQ-9, provides an easy-to-interpret single score of physical and emotional symptoms that accurately indicates the presence (or lack of) and severity of the disorder, assisting in a diagnosis.

"You don't treat hypertension or diabetes without measuring and monitoring a patient's blood pressure with a blood pressure cuff or the hemoglobin in the blood with an A1C test," said Kurt Kroenke, MD, a co-author of the new study, the developer of the PHQ-9 and a Regenstrief Institute Research Scientist and an Indiana University School of Medicine faculty member. "Similarly, with depression, you need to be able to measure and monitor the presence of both physical and emotional symptoms and their severity.

"This study has shown that the free, easy-to-use PHQ-9, which can be administered in person, via telehealth or on a computer, provides a single, combined score of physical and emotional symptoms that is a good indicator of presence and severity of depression, enabling both physicians and patients to track scores and respond appropriately."

The study found the PHQ-9's combined physical and emotional symptom score to be accurate regardless of sex, age and language of translation. PHQ-9 scores are based on patient self-rating of physical and emotional symptoms over the past two weeks including low mood, fatigue, sleep problems, inability to concentrate, loss of appetite and lack of interest in one's usual activities. The PHQ-9 employs a four-point rating scale, from 0 for "not at all" to 3 for "nearly every day."

"By determining that the PHQ-9's single score of physical and emotional symptoms is a good indicator of presence and severity of depression, this study definitively shows that two scales, one for physical symptoms and one for emotional symptoms, with the ensuing need to somehow balance the two scores, are not necessary, making it easier to evaluate and treat depression," said Dr. Kroenke, a father of the growing field of symptomology.

The 58,272 study participants came from seven countries—the U.S., France, Germany, Israel, New Zealand, Spain and Switzerland—and completed the PHQ-9 in English, Spanish, French, German or Hebrew. The research is published in Psychological Assessment.