Both the original Patient Health Questionnaire and later variants are public domain resources; no fees or permissions are required for using or copying the measures.
[9][10][11] The original Patient Health Questionnaire contains five modules; these contain questions about depressive, anxiety, somatoform, alcohol, and eating disorders.
The PHQ-9 (DEP-9 in some sources[13]), a tool specific to depression, scores each of the 9 DSM-IV related criteria based on the mood module from the original PRIME-MD.
Firstly, traditional methods of diagnosing somatoform disorders would only capture about 20% of true cases due to the number of symptoms required to meet a diagnosis.
[8]: 3 [21] The PHQ-A is a four module self-report to evaluate depression, anxiety, substance use and eating disorders in adolescent primary care patients.
[2] All versions of the PHQ are self reports and, consequently, are subject to inherent biases, including social desirability[38] and poor retrospective recall.
Depending on the time period in question, this may or may not require a revision (i.e., if you are interested in depression over the last six months, you might alter the instructions), which could impact the validity of the measure.
The scoring thresholds recommended are influenced by the samples in which they were validated and correspond with different levels of sensitivity and specificity,[41] which may or may not match well with the intended use of the scale.