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Rationale

Sun (2020) describes the PHQ-9 as an effective, reliable, effective, simple and rapid tool which therapists can use for screening and evaluating the severity of a client's depression.

 

How it measures it

This instrument has nine items. Each one is scored 0 to 3, providing a 0 to 27 severity score

 

Validity

Sun et al. (2020) explains that in a test of 109 depressed patients, the PHQ-9 tested at a Cronbach’s α coefficient of .892 and that PHQ-9 shows good validity.

 

Reliability

Sun et al. (2020) tested reliability by conducting a repeat assessment two weeks after the initial measurement. This included 54 of the 109 patients (49.5 %). The resulting pearson correlation analysis indicated a test-retest reliability coefficient score of .737 for the total scores (P < 0.01). Additionally, the test-retest reliability coefficient for each individual item score ranged from 0.552–0.728 (P < 0.01). Sun et al. (2020) notes that these findings indicate a significant correlation between the patients' scores in the two tests. Sun et al. (2020) concludes that PHQ-9 shows good reliability.

 

Responsiveness, Sensitivity to Change

Sun et al.'s (2020) research points to the PHQ-9 instrument as appropriate for evaluating the psychological characteristics of patients who are experiencing depression. However Sun et al. (2020) explains that it is not sensitive to changes in symptoms. This is why the researcher will not be using the PHQ-9 to measure changes from pre- to post-depression levels, but solely as a measurement of whether the client's depression is sufficiently significant for inclusion in the study.

 

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Sun, Y., Fu, Z., Bo, Q., Mao, Z., Ma, X., & Wang, C. (2020). The reliability and validity of PHQ-9 in patients with major depressive disorder in psychiatric hospital. BMC psychiatry, 20(1), 474. https://doi.org/10.1186/s12888-020-02885-6

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