The PHQ-9 and PHQ-2 assessments are both components of the longer Patient Health Questionnaire, which offers psychologists a concise way to self-administer an evaluation to assess depression. The assessment incorporates DSM-IV depression criteria, which are clinically significant behavioral or psychological patterns that occur in individuals (i.e. depressed mood, poor appetite, etc.), along with other major depressive symptoms into a brief self-reported assessment that is commonly used for screening, diagnosis, and selecting and monitoring treatment. Above is an example of how this assessment is generally found in physicians offices and other healthcare centers.
Both the PHQ-9 and the PHQ-2 have been significantly studied and researched, all pointing to good reliability and validity. Additionally, it is very easily adaptable for patients with major depressive disorder (MDD) in psychiatric hospital settings. The assessment is simple, rapid, effective, and reliable as a tool for screening and evaluating the severity of depression in patients.
Because both versions of the PHQ are self reports, they are subsequently subject to inherent biases, mainly in response bias. This means that for the individual filling out the assessment, it is entirely up to them to tell the truth or not in their responses.
The main type of response bias that these assessments face is social desirability bias, where patients tend to answer in a manner that they think will be more favorable to others, rather than answering truthfully. Essentially, they will over-report the good behavior and under-report or even leave out the bad behavior or feelings they might actually be experiencing.
In addition, the varying time period of these assessments could also limit the results, as answers could be subject to change over time. The PHQ9 specifically asks about the last 4 weeks, whereas the entire Patient Health Questionnaire can ask about various time periods from the last 2 weeks to the last 6 months.
When it comes to language barriers, the PHQ-9 is available in 49 different languages, but it has not been validated in all those languages yet. However, there are several validated alternative assessments available in primary care settings for those with language or cognitive barriers.
Despite some of the inevitable biases that exist within this assessment, the PHQ-9 and PHQ-2 are some of the most validated tools in mental health and have been proven to be very powerful in assisting clinicians with diagnosing depression and monitoring response to treatment.