Reliability and Validity of the PHQ-9 in Portuguese Women with Breast Cancer


Depression is often overlooked in oncology practice. Depressive module PHQ-9 was not studied in Portuguese cancer patients, despite its brevity and comparable psychometric proprieties to other depression scales. Which are the psychometric properties of the Portuguese version of the PHQ-9 for use with women with breast cancer? Reliability, sensitivity to change and the construct validity will be studied. The purpose of this study is to assess the psychometric properties of the Portuguese version of the PHQ-9 for use with women with breast cancer. This study intends to evaluate the reliability, the sensitivity to change and the construct validity of the PHQ-9 in a Portuguese Breast Cancer women sample.It was reproduced a principal component analysis and explored the reliability and validity of the questionnaire. The validation used a sample of 63 Portuguese women with breast cancer. A test-retest was conducted in 45 women, after 8 weeks. Construct validity was analysed.PHQ-9 scores ranged from 0-27, with a mean score of 4,92 (SD= 4,63). The scale presented adequate internal consistency (α = .86) and test retest reliability (ICC= .87). It also presented good construct validity, as overall scores and severity levels were strongly associated with functional and symptoms subscales. The principal component analysis explains 48.42% of the variance.The validation process of the Portuguese PHQ-9 version shows metric properties similar to those in international studies, suggesting that it measures the same constructs, in the same way, as the original version. Data provided evidence for the validity of the PHQ-9 as a brief measure of depression severity in Portuguese women with breast cancer.

Keywords: Breast cancer, PHQ-9, depressive symptoms, psychometric


Depression is the greatest cause of incapacity in the world according to World Health Organization (Murray& Lopez, 1996). Given the high prevalence and its consequences to the general population, this mental illness is considered to be one of the priority goals of the National Health Plan, which gives rise to the urgent need for an integrative assessment and for a management approach in the scope of mental illness (Ministério da Saúde [Health Ministry], 2004). The lifetime prevalence rates for major depressive disorder in the general population are high, about 16.6% (Kessler, Chiu, Demler, & Walters, 2005), and prevalence rates in cancer patients are even higher (Hinzet al., 2010; Van’t Spijker, Trjsburg, & Duivendoorden, 1997), ranging from 0% to 38% for major depression, and 0% to 58% for depression spectrum syndromes (Massie, 2004). According to Massie (2004), breast cancer is one of the cancer types that is highly associated with depression (1.5%-46%). Depression has an impact on quality of life and on the satisfaction with, and participation in medical treatment (Bui, Ostir, Kuo, Freeman & Goodwin, 2005; Skarstein, Aass, Fossa, Skovlund, & Dahl, 2000). Despite these facts, depression is often overlooked (Fallowfield, Ratcliffe, Jenkins, & Saul, 2001) and untreated in oncology practice, especially when it is most needed (Söllner et al., 2001; Passik et al., 1998).

The use of case-finding instruments for the detection of depression is strongly suggested (Mitchell, 2007). There are a number of instruments to detect depression symptoms, but the Patient Health Questionnaire’s depressive module (PHQ-9) is half the length of many of the other depression scales and has comparable sensitivity and specificity. The Patient Health Questionnaire (PHQ; Kroenke, Spitzer, & Williams, 2001) is a self-report instrument developed to screen for psychiatric disorders in primary care and assess eight specific disorders based on DSM-IV (APA, 2002) criteria. It was validated in primary care patients and it has been used with cancer patients (Ell et al., 2007; Spitzer, Kroenke, & Williams, 1999). The nine items for depression (PHQ-9) and the 22 items for anxiety disorders may easily be translated into oncology settings, unlike the modules for somatoform disorder and eating disorders (Pirl, 2010). The diagnostic validity of PHQ has been established in studies involving a large number of patients (Spitzer et al., 1999; Spitzer, Williams, Kroenke, Hornyak, & McMurray, 2000).

The PHQ-9 consists of a depression module with nine items, using a 4-point response scale, ranging from “0” (not at all) to “3” (nearly every day) to report each of the 9 DSM criteria. It can be scored both categorically, to provide likely diagnoses, and continuously, to give level of symptoms. To meet the criteria for a probable major depression diagnosis patients must state having the two items for low mood and anhedonia, and report having at least five other symptoms “at least half of the time” or more, which is consistent with DSM-IV criteria (Pirl, 2010). As a severity measure, the PHQ-9 score can range from 0 to 27, with high scores being related to greater severity of depression (Kroenke et al., 2001). It also includes a final item asking patients who reported any problems: “How difficult have these problems made it for you to do your work, take care of things at home, or get along with other people?”. Regarding psychometric characteristics, the internal consistency is excellent, with a Chronbach’s alpha of .89 in the PHQ Primary Care Study and .86 in the PHQ Obstetric-Gynaecological Study (Kroenke et al., 2001). Different studies (Cameron, Crawford, Lawton, & Reid, 2008; Lee, Schulberg, Raue, & Kroenke, 2007) found good internal consistency reliability. The test-retest reliability has been reported with a Correlation Coefficient from .71 (Omoro, Fann, Weymuller, Macharia, & Yueh, 2006) to .92 (Pinto-Meza, Serrano-Blanco, Penarrubia, Blanco, & Haro, 2005). Convergent validities were also found, from .56 (Lotrakul, Sumrithe, & Saipanish, 2008) to .74 (Changsu et al., 2008). A meta-analysis of Gilbody, Richards, Brealey and Hewitt (2007) found a high sensitivity (.80) and specificity (.92). Moreover, a systematic review of Wittkampf, Naeije, Schene, Huyser and van Weert (2007) found a PHQ-9 sensitivity of .77 and a specificity of .94. We found studies with sensibilities ranging from .5 (Carballeira et al., 2007) to 1 (Osório, Mendes, Crippa, & Loureiro, 2009), and with specificities ranging from to .76 (Carballeira et al., 2007) to .98 (Yeung et al., 2008; Osório et al., 2009). More recently in a systematic review, Kroenke, Spitzer, Williams and Löwe (2010) reaffirm that PHQ-9 has a good sensitivity and specificity for detecting depressive disorders, as well as a good sensitivity to change, which lead to the conclusion that this is a brief, well-validated measure for detecting and monitoring depression. In this study the authors further restated the PHQ-9 cut-off points of 5, 10 and 15 for mild, moderate and severe symptom levels, respectively.

Several PHQ-9 versions were validated in different samples and in diverse languages and cultural contexts, demonstrating proprieties that confirm it as a reliable scale to assess depressive symptoms, namely in: primary health care (Cameron et al., 2008; Diez-Quevedo, Rangil, Sanchez-Planell, Kroenke, & Spitzer, 2001; Liu et al., 2011; Osório et al., 2009; Yu, Tam, Wong, Lam, & Stewart, 2012); students (Adewuya, Ola, & Afolabi, 2006; Granillo, 2012); elderly population (Changsu et al., 2008). Moreover it has been adapted to different languages and cultures, such as Brazilian (Osório et al., 2009), Thai (Lotrakul et al., 2008), Greek (Karekla, Pilipenko, & Feldman, 2012), Saudi Arabian (Becker, Zaid, & Faris, 2002), Taiwanese (Liu et al., 2011), Chinese (Yeung et al., 2008), Korean (Changsu et al., 2008), Spanish (Diez-Quevedo et al., 2001), Mexican (Donlan & Lee, 2010), French (Carballeira et al., 2007), Nigerian (Adewuya et al., 2006), Turkish (Güleç, Güleç, Simsek, Turhan, & Sünbül, 2012) and Japanese (Yu et al., 2012). The PHQ-9 has been reported to have a single factor in several previous studies (Cameron, Crawford, Lawton, & Reid, 2008; Dum, Pickren, Sobell, & Sobell, 2008; Graves & Bombardier, 2008; Hansson, Chotai, Nordstöm, & Bodlund, 2009; Yu et al., 2012), including a study involving more than 5000 primary care patients (Huang, Chung, Kroenke, Delucchi, & Spitzer, 2006). Exceptions are typical among participants with Spinal Cord Injury, in which the most of the studies have suggested a 2-factor structure, differentiating somatic and non somatic symptoms (Krause, Reed & McArdle, 2010; Richardson, & Richards, 2008). Kalpakjian et al. (2009), after comparison of 1- and 2-factor solution, concluded that the 1-factor solution represented a better fit, because of sex congruence.

Problem Statement

Despite its strong psychometric properties and widespread use in primary care, there is scarcity of information when used in cancer patients, as it was concluded in the major recent review of screening questionnaires for psychological distress in cancer patients (Vodermaier, Linden, & Siu, 2009). The few studies reported, however, good psychometric properties of this scale with this population. For instance, even the original validation encloses obstetrics and gynaecology patients and found to have strong psychometric proprieties (Kroenke et al., 2001). The PHQ-9 also demonstrated adequate reliability as well as concurrent and divergent validity in a study of head and neck cancer patients (Omoro et al., 2006) and in a study that used a touch screen computerized version of the questionnaire with 342 cancer patients (Fann et al., 2009). A more recent study (Johns et al., 2013) found an internal consistency of .81 and good correlations with other measures of depressive symptoms, which lead them to consider it as a reliable and valid depressive measure in adults with cancer, as well as a useful measure for monitoring depression therapy and outcomes in this population.

Research Questions

Which are the psychometric properties of the Portuguese version of the PHQ-9 for use with women with breast cancer? Reliability, sensitivity to change and the construct validity will be studied.

Purpose of the Study

The purpose of this study is to assess the psychometric properties of the Portuguese version of the PHQ-9 for use with women with breast cancer. This study intends to evaluate the reliability, the sensitivity to change and the construct validity of the PHQ-9 in a Portuguese Breast Cancer women sample.

Research Methods

  • Sample

The participants of the study, 63 women with breast cancer, were recruited from the Reach to Recovery Movement of the Portuguese Cancer League (Mean age= 60.46, SD=10.88, Min=30, Max=85). To be eligible to participate, patients had to be adults (older than 18 years) and have a breast cancer diagnosis history. Patients were excluded if they had psychotic disorder, neurological disease or substance abuse that might compromise their ability to complete the questionnaires, or if they declined to participate voluntarily after informed consent. Also, we excluded those patients who did not answer more than 50% of the assigned questionnaires. The majority of the sample was married (81%), attended tertiary education (31.7%) and retired (85.7%). Regarding the clinical characteristics, the sample is composed by survivors (88.9%) and patients in the treatment phase (11.1%), given that the majority: self-detected their cancer (39.7%); realized mastectomy (73%); did axillary lymph node dissection (58.7%), chemotherapy (68.3%) and did no radiotherapy (54%). Just 11.1% had cancer recurrence. All demographic and clinical variables are detailed in Table 1. A total 45 women participated in the test-retest study, after 8 weeks. Moreover, 2 women did not answer completely to the questionnaires used for study’s the construct validity.The sample of participants consisted of 33 older adults, aged from 65 to 94 years old (M=82.18, SD=7.85), participated in 2 groups, group with intervention (GI, n=16) and a waiting group (GC, n=17).

Table 1 - Table 1.
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The questionnaire covered the socio-demographic information, such as age, gender, marital status and study cycle, as well as, the depressive symptoms and the quality of life. Cancer-specific variables included treatment status (on or off treatment), way of cancer detection and type of treatments received.

Depressive symptoms were assessed by two measures, the PHQ-9 (in study on this work) and the Hospital Anxiety and Depression Scale [HADS] (Zigmond & Snaith, 2003). HADS consists of two subscales, one assessing anxiety, and one measuring depression, both with seven items, which are scored separately. Each item is answered by the patient on a 4-point (0 – 3) response scale, thus, the possible scores range from 0 to 21 for anxiety and 0 to 21 for depression. The HADS manual indicates that a score between 0 and 7 is ‘‘normal’’, between 8 and 10 ‘‘mild’’, between 11 and 14 ‘‘moderate’’, and between 15 and 21 ‘‘severe’’. Zygmond and Snaith (2003) posit a score of 11 or higher indicating probable presence (‘‘caseness’’) of a mood disorder and a score of 8 – 10 being just suggestive of the presence of the respective state. The original version, as does the Portuguese version (Pais-Ribeiro et al., 2007), presents adequate psychometric characteristics.

The European Organization for Research and Treatment of Cancer Quality of Life Questionnaire Core-30 [EORTC QLQ-C30] (Aaronson et al., 1993) was used to assess the QOL. It is a 30-item questionnaire, 24 of the items constitute nine multi-item scales, and six items are single-item symptom measures. The scales are constructed by sum of the scores of the items. Multi-item subscales and single items intend to reflect the multidimensionality of the QOL construct, namely: five functional subscales (physical, role, cognitive, emotional, and social); a global health/QOL subscale; three symptom subscales (fatigue, pain, and nausea/vomiting); and single items for the assessment of additional symptoms commonly reported by cancer patients (dyspnoea, appetite loss, sleep disturbance, constipation, and diarrhoea); one more item related to the perceived financial impact of cancer and cancer treatments. All the items are scored on 4-point Likert type scale, ranging from 1 “not at all” to 4 “very much”, except for the two items of the global health/quality of life subscale, that uses a modified 7-point linear analogue scale. A high score for functional scales and global health status/QOL represents a high/healthy level of functioning and quality of life, in opposition to symptom subscales and single items. The original version, as does the Portuguese version (Pais-Ribeiro, Pinto, & Santos, 2008), of EORTC QLQ-C30 presents adequate psychometric characteristics.

All statistical analyses were conducted with SPSS, version 19.0. We adhered to the classical test theory to examine the reliability and validity of the PHQ-9, guided for Carretero-Dios and Pérez (2007), and similarly to the Kenyan validation by Omoro et al. (2006). Reliability was established by assuring both internal consistency and testretest reliability. The validity was evaluated by the construct validity. We hypothesized that higher PHQ-9 scores were related to lower results in the functional scales of quality of life and higher symptoms (evaluated by HADS and QLQ C-30 symptoms subscales). The cut-off points suggested by the original authors were the ones adopted, to identify minimal (0-4), mild (5-9), moderate (10-14), moderately severe (15-19), and severe (20-27) depression. Construct validity of the PHQ-9 as a measure of depression severity was assessed by examining functional sub-scales and symptoms sub-scales (evaluated by HADS, QLQ C-30 and supl. BR-23), over the 5 PHQ-9 intervals. To test the differences of the 5 groups of severity on the quality of life, we opted for a Jonckheere-Terpstra test, which is similar to the Kruskal-Wallis test, but incorporates information about whether the order of the groups is meaningful. In parallel, in order to evaluate the differences of the 5 groups of severity of PHQ-9 on the 4 depression levels evaluated by the HADS, we chose to use the Pearson’s chi-square test. We used the 4 groups of severity of depression: normal (0 to 7); mild (8 to 10); moderate (11 to 14) and severe (15 to 21), suggested by the HADS authors.

Adaptation to the Portuguese language

The translation used a two-person English-Portuguese translation, a two-person retroversion, and a discussion group to achieve full consensus for the lexical and cultural equivalence. The content validity analysis was performed by two psychologists. After lexical equivalence and content validity were defined, a cognitive debriefing analysis was performed with subjects from the lower educational levels and from the oldest groups of potential patients. After the final version was defined, we chose a face format for the questionnaire identical to theoriginal.


PHQ-9 scores ranged from 0-27, with a mean score of 4.92 (SD= 4.63). The majority (53.1%) presents scores, which indicate minimal depression severity symptoms, 34.4% present mild severity, 9.4% moderate, and 1.6% severe.

6.2 Reliability

Chronbach’s alpha was performed to identify the internal consistency of the scale. A good Chronbach’s alpha of .86 was found. We also observed that none of the items correlated less than .52 with the total score (above the required minimum of .30), and none of the items would affect reliability if they were deleted (see Table 2).

Table 2 - Table 2.
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6.3 Test-retest

In order to inspect test-retest correlation, the instruments were administered twice, with an interval of 8 weeks, in 45 breast cancer women. The intra-class correlation coefficient was excellent (ICC= .87).

6.4 Construct validity

Examining the PHQ-9 as a continuous variable, its correlation with the sub-scale of depression of HADS was .46 (p<.001). It also correlates significantly with sub-scale of anxiety of HADS, .42 (p<.001). This data can indicate that PHQ-9 is also sensitive to anxiety states. PHQ-9 also presented significant correlations with some sub-scales of EORTC QLQ-C30 and Supl. BR-23, namely negative correlations with: role functioning (rS= -.29, p<.05), emotional functioning (rS= -.51, p<.001), cognitive functioning (rS= -.31, p<.05), sexual enjoyment (rS= -.47, p<.05), and future perspective (rS= -.36, p<.05). Significant positive correlations were also obtained in the following sub-scales: fatigue (rS= .52, p<.001), constipation (rS= .29, p<.05), systemic therapy side effects (rS= .33, p<.05), breast symptoms (rS= .53, p<.001) and arm symptoms (rS= .35, p<.05). The associations between increasing PHQ-9 depression severity scores and EORTC QLQ C-30, BR-23 and depression and anxiety severity of HADS are shown in the Table 3, 4 and 5.

Table 3 - Table 3.
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In Table 3 it is possible to observe that there are significant differences between the severity of groups regarding role functioning, emotional functioning and cognitive functioning. The negative z-value should also be noted, given that it indicates a trend of decreasing medians with the increment of depression severity. Several significant differences are also observed in the severity groups regarding symptoms, namely, fatigue, dyspnoea and constipation, as shown in Table 4. In this case, the z-value is positive, indicating a trend towards ascending medians with the increment of depression severity.

Table 4 - Table 4.
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The same pattern of significant differences between the groups’ severity is observed for quality of life, by the general QLQ C-30 scale, and is also observed in the breast cancer module (BR-23), as presented in Table 5. Only one functional scale (future perspective) and one symptom scale (upset by air loss) did not present significant differences for severity groups. The sign of z-value is the same as that for functional and symptoms scales of the QLQ C-30 measure, indicating a trend toward ascending medians with the increment of severity for functional scales and a trend of decreasing medians for symptoms scales. The relationship between depression levels of PHQ-9 and levels of HADS shows that PHQ-9 groups differ significantly on depression levels of HADS, but not on the anxiety levels of HADS (Table 6).

Table 5 - Table 5.
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Table 6 - Table 6.
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a. Multiple modes exist. The smallest value is shown.

6.5 Factorial validity

It was performed exploratory factor analysis to identify the number of factors and the magnitude of the factorial loading, using a principal component analysis with Kaiser Normalization for the total patients (n= 63). We found a single factor solution, which explains 48.42% of the variance, with all the items presenting loadings above .40. The factor analysis results provide further information about the proprieties of the PHQ-9. The determinant of the correlation matrix is .01 (greater than necessary value, .0001). The observation of the correlation matrix also leads us to conclude that all the items correlate fairly well with all other, and no correlation coefficients are particularly large. The value of KMO for multiple variables, as a measure of sampling adequacy, was very good (.83), therefore we should be confident that the factor analysis is appropriate for these data. Bartlett’s test of sphericity was significant (p<.001), which indicates that Rmatrix is not an identity matrix, thus, the sample is adequate allowing for a factorial analysis.


In this study we completed a translation, test of reliability, construct validation and factorial validity of the Portuguese PHQ-9 depression scale in a breast cancer sample. Data provided evidence for the validity of the PHQ-9 as a brief measure of depression severity in Portuguese women with breast cancer. A first principal component analysis results on a single factor solution explaining 48.42% of the variance. The majority of studies of the factor analysis of PHQ-9 holds a single factor solution (Cameron et al., 2008; Dum et al., 2008; Graves & Bombardier, 2008; Hansson et al., 2009; Huang et al., 2006; Kalpakjian et al., 2009; Yu et al., 2012), with explained variances from 38.9% (Huang et al., 2006) to 59.57% (Dum et al., 2008). A onedimensional solution would be suggested, theoretically, by the DSM-IV. Exceptions reported a two factor solution (Krause et al., 2010; Richardson, & Richards, 2008). Our results lend support to the notion of a single-factor structure for the symptoms assessed by the PHQ-9.

Reliability of .86 is exactly the same value obtained in the original study, which includes an obstetrics-gynaecology cancer sample (Kroenke et al., 2001). This value is argued as excellent, because when the test is used for diagnostic or classification purposes, the minimum value advisable should be around .80 (Nunnally & Bernstein, 1995). This measure presents good test-retest reliability, with a correlation of .84. This correlation is better than other versions used with cancer patients, for instance .71 obtained by Omoro et al. (2006), but lower than versions used with other samples (Adewuya et al., 2006; Liu et al., 2011; Pinto-Meza et al., 2005).

The construct validity was established by the strong association between PHQ-9 scores, HADS and Quality of life scores. The results demonstrate that higher PHQ-9 scores are related to lower functional scales of quality of life, and increased symptoms.

Similarly to original validation (Kroenke et al., 2001), we verified a strong association between increasing PHQ-9’s depression severity scores and the worsening of functional scales, evaluated by QLQ C-30 and BR-23. We also obtained significant decreases for the scales that previous studies have shown should be most strongly related to depression, i.e. mental health (emotional functioning, cognitive functioning, future perspective) and role functioning. The association with symptoms’ sub-scales, especially with the depression sub-scale of HADS, was also expected and showed the extent to which both instruments measure the same construct.

Some limitations of the present study should be pointed out. The size and the composition of the sample, which consisted exclusively of women, prevent the results from being generalized to other samples or to the general population. Accordingly, future studies involving different and larger samples are still necessary. Samples with higher levels of depression severity are still necessary too. The data are limited to self report.

It would be interesting to have external data that could be used, as a structured interview, to determine the sensibility and specificity of the measure. To perform a confirmatory factor analysis in addition to exploratory factor analysis, with a Portuguese larger sample, would be a good suggestion for future studies.

To our knowledge, this is the first study to investigate the PHQ-9 in Portuguese cancer patients. Other studies with cancer patients are encouraged. As main implication to the research and clinical practice, this study contributes with the adaptation and validation of an instrument that has characteristics (namely brevity, adequate psychometric characteristics and diagnostic potential) that are useful for the assessment and emotional screening of cancer patients.


This study was developed under the scope of a PhD fellowship granted by Fundação para a Ciência e Tecnologia [Foundation for Science and Technology of Portugal] (Reference Number: SFRH / BD / 44296 / 2008). The authors would like to thank Reach to Recovery Movement of Portuguese Cancer League [Movimento Vencer e Viver da Liga Portuguesa contra o Cancro] for allowing the access to breast cancer patients. The authors would also like to thank to Raquel V. Oliveira (psychologist and native speaker) for proof reading the paper prior to its submission.


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Torres, A., Monteiro, S., Pereira, A., & Albuquerque, E. (2016). Reliability and Validity of the PHQ-9 in Portuguese Women with Breast Cancer. In S. Cruz (Ed.), Health & Health Psychology - icH&Hpsy 2016, vol 13. European Proceedings of Social and Behavioural Sciences (pp. 411-423). Future Academy.