The ‘quick and dirty’ PHQ-9 questionnaire was developed to sell more Zoloft.
The nine-question Patient Health Questionnaire, better known as the PHQ-9, was the brainchild not of researchers, but a marketing executive.
As reported this week in an investigative piece by US health news outlet Stat, in the early 1990s Pfizer was searching for a new way to encourage primary care doctors to prescribe its newly-released antidepressant, Zoloft (sertraline).
Enter marketing man Howard Kroplick, who persuaded the pharmaceutical giant to commission research into a simple checklist which could be used to identify depression, leading to more prescriptions for and sales of Zoloft.
At that stage, mental illness was still something of a taboo subject and primary care clinicians weren’t always confident in prescribing antidepressants.
By making a quick and easy-to-use tool like the PHQ-9, the Stat article argues, Pfizer was able to broaden the base of potential Zoloft prescribers by creating a sense of certainty and accuracy around diagnosis.
The questionnaire was Mr Kroplick’s idea but funded by Pfizer and developed and validated by psychiatrist Professor Robert Spitzer, clinical psychiatric social work researcher Professor Janet Williams and primary care clinician Dr Kurt Kroenke.
While the PHQ-9 stood up to validation, it’s since been found to have a high false positive rate and is more than twice as likely to indicate that patients are potentially depressed compared to a physician-conducted clinical evaluation.
People with other conditions – such as ADHD, addiction, eating disorders and trauma – are also likely to test positive for depression when evaluated using the PHQ-9.
Dr Brooke Levis, who co-authored a 2020 review of the PHQ-9, told Stat it was “a quick and dirty tool”.
According to Stat, overstretched American clinicians can put too much stock in the PHQ-9’s efficacy and patients often end up on a medication they don’t need.
While most Australian GPs use the 10-question Kessler psychological distress scale (K10), The Medical Republic understands that the PHQ-9 is growing in popularity among clinical psychologists.
Dr David Hallford, a board member of the Australian Clinical Psychology Association, told TMR that the PHQ-9 was mainly used when screening for depression specifically.
“It really only looks at the symptoms of major depression, but it’s quite good at determining whether someone might have a diagnosis on further assessment,” he said.
In practice, Dr Hallford said, it’s best to limit use of the PHQ-9 to screening for depressive symptoms.
The K10 isn’t perfect either.
“The K-10 doesn’t actually identify specific disorders … it’s a tool that was created to measure general mental distress or psychopathology,” Dr Hallford said.
“[Researchers] basically got a whole bunch of different items and tried to find the smallest set that would be best at detecting whether or not someone might have a serious mental illness.
“It measures things that look a bit like depression or anxiety: fatigue, worry, sadness, things like that.”
The third commonly used screening tool, the Depression Anxiety and Stress Scale 21 (DASS-21), ostensibly measures the core symptoms of depressive disorders, anxiety disorders and stress.
“The DASS gives a score that can be interpreted as mild, moderate, elevated or severely elevated, but the DASS is actually not well validated for its correspondence with diagnoses,” Dr Hallford said.
“It gives you a score … but we don’t really know exactly where on that tool might indicate a likely diagnosis.”
One of the limitations of all mental health screening tools is that they tend to capture a moment in time, not the whole picture.
“Someone scoring higher or lower on a measure doesn’t really reflect more broadly how they’re doing,” Dr Hallford said.
“If someone comes in and they’ve had a fight with their partner or something, they’re likely to be feeling a lot worse and then they may score over the line on the PHQ-9.”
Dr Tim Jones, a Tasmanian-based GP with special interest in mental health, told TMR that most Australian GPs would likely be conducting a comprehensive assessment of patients’ mental health already, and only using screening tools to gather additional information as needed.
“They do have some useful clinical utility,” he said.
“I think sometimes for patients, as well, it helps for them to get an idea of how severe their symptoms might actually appear when we when we start logging them out and putting them in front of us.”
It’s also useful, Dr Jones said, to use screening tools to track a patient’s mental health over time and inform ongoing treatment.
“It is really nice sometimes in follow up to repeat that questionnaire and see which areas might be improving and which ones are still outstanding, to further tailor what your next steps of treatment and support might be,” he said.
This article has been amended to clarify that TMR spoke with Dr Tim Jones.
