PHQ-9 Reliability and Validity in University Students: Evidence From Pakistan

The Patient Health Questionnaire-9 (PHQ-9) showed good reliability and useful psychometric performance among university students in a recent Pakistani study of 602 undergraduates. Its internal consistency was strong, its items differed meaningfully in how well they distinguished depressive symptom severity, and measurement invariance analyses supported comparisons between medical and non-medical students. These findings strengthen the case for using the PHQ-9 as a research and screening instrument in Pakistani university populations, while also reinforcing an essential limitation: a PHQ-9 score measures depressive symptoms and does not, by itself, establish a clinical diagnosis.

By Taimoor Asghar

Why PHQ-9 reliability and validity matter in university students

The PHQ-9 is one of the most widely used questionnaires for assessing depressive symptoms. It contains nine items corresponding to core depressive symptoms and asks respondents how frequently they have experienced each symptom over the preceding two weeks. Its brevity makes it attractive for university surveys, primary care screening, epidemiological research and repeated symptom monitoring.

However, widespread use does not automatically mean that an instrument performs identically in every population. A questionnaire developed and initially evaluated in one setting may behave somewhat differently when used with younger adults, students, different languages, different educational groups or populations with different cultural interpretations of emotional and physical symptoms.

That is why local psychometric evidence matters. When researchers use the PHQ-9 among university students in Pakistan, important questions include whether its items behave coherently as a scale, whether some items provide more information than others, and whether comparisons between different student groups are psychometrically defensible.

A 2026 BMC Psychology study addressed several of these questions while examining mental-health symptoms among medical and non-medical university students in Lahore. The published BMC Psychology study of the PHQ-9 and DASS-21 in Pakistani university students included 602 undergraduates and applied reliability analysis, item response theory, measurement invariance testing and symptom-network methods alongside conventional comparisons of symptom scores.

What does PHQ-9 reliability actually mean?

Reliability describes the consistency or precision of a measurement. For a multi-item questionnaire such as the PHQ-9, one commonly reported form is internal consistency: the extent to which the individual questions behave as parts of a related construct.

The Pakistani study reported Cronbach’s alpha values ranging from 0.82 to 0.88 across the scales examined, including the PHQ-9 and DASS-21 domains. An alpha in this range is generally consistent with good internal consistency for group-level research. In practical terms, the PHQ-9 items were sufficiently related to function together as a coherent measure of depressive symptom burden in this sample.

This is reassuring, but reliability should not be misunderstood. A high alpha does not prove that a questionnaire diagnoses depression correctly. It also does not establish that every item is equally useful, that the scale has only one psychological dimension in every population, or that the same numerical cut-off has identical diagnostic meaning across all groups.

Why a very high alpha is not the goal

Researchers sometimes interpret a larger Cronbach’s alpha as automatically better. That is too simplistic. Alpha is influenced by both the relationships among items and the number of items in a scale. Extremely high values can sometimes indicate substantial item redundancy rather than superior measurement.

The more useful question is whether reliability is adequate for the intended purpose while the items still capture clinically relevant aspects of the construct. The Pakistani findings support adequate internal consistency without implying that reliability alone establishes the PHQ-9’s validity.

Reliability is not the same as validity

Reliability asks whether a measure operates consistently. Validity asks whether the interpretation made from its scores is supported by evidence. A scale can be reliable while still failing to measure the intended construct accurately in a particular context.

Modern psychometric evaluation therefore draws on several forms of evidence rather than relying on one statistic. For the PHQ-9, useful evidence can include relationships among items, associations with related measures, item-level discrimination, consistency across groups, diagnostic performance against clinical assessment and whether predicted patterns appear in external variables.

The 2026 Pakistani study did not replace a diagnostic validation study using structured psychiatric interviews. Instead, it provided several complementary forms of psychometric evidence within a university sample. This distinction matters when interpreting what the results can and cannot establish.

What the Pakistan study examined

The cross-sectional investigation included 602 undergraduate university students in Lahore, Pakistan: 424 medical students and 178 non-medical students. Participants completed the PHQ-9 and the 21-item Depression Anxiety Stress Scales, or DASS-21.

The researchers went beyond simply calculating average scores. Their analyses included descriptive statistics, group comparisons, multivariable regression, reliability assessment, confirmatory factor analysis for the DASS-21, graded-response item response theory, symptom-network analysis and measurement invariance testing.

This multi-method approach is useful because a questionnaire can be examined at several levels. A total-score reliability coefficient describes the scale broadly, item response theory evaluates the behavior of individual questions along an underlying severity continuum, and measurement invariance examines whether group comparisons are supported by similar measurement properties.

PHQ-9 internal consistency was good

The study’s reliability estimates provide straightforward support for use of the PHQ-9 in this population. Cronbach’s alpha across the evaluated scales ranged from 0.82 to 0.88, indicating good internal consistency.

For university mental-health research, this means investigators can have reasonable confidence that the PHQ-9 items function together rather than representing a collection of essentially unrelated symptoms. It supports calculation and interpretation of a total symptom score for research purposes in comparable student populations.

Still, internal consistency is sample-dependent. A reliability coefficient observed among these Lahore undergraduates should not automatically be assumed for every Pakistani population. Adolescents, older adults, clinical psychiatric populations, students in other provinces and respondents completing translated versions may produce different psychometric results.

Item response theory revealed that PHQ-9 items were not equally informative

One of the most informative aspects of the study was its use of item response theory, specifically a graded-response model. Unlike a reliability coefficient that summarizes a scale globally, item response theory examines how individual questionnaire items behave across different levels of the underlying trait.

An important parameter is item discrimination. In simplified terms, discrimination describes how sharply an item differentiates between respondents who are at slightly different positions on the underlying symptom-severity continuum.

In the Pakistani sample, items involving self-worth, concentration and feeling down were among those with the strongest discrimination, while the loss-of-interest or anhedonia item showed the lowest reported discrimination, with a discrimination parameter of 0.468.

This does not mean the interest item should be removed from the PHQ-9. Anhedonia is clinically important, and individual psychometric parameters depend on the population and statistical model. Rather, the result illustrates why item-level analysis adds information that Cronbach’s alpha cannot provide: different symptoms can contribute differently to measurement precision within a particular student population.

Why item discrimination may vary between populations

Several mechanisms can potentially influence item behavior. University students may interpret sleep, appetite, concentration and fatigue differently because these experiences can also be affected by examinations, irregular schedules, workload and lifestyle. Cultural expectations may influence how emotional symptoms or feelings of failure are understood and reported. Differences in symptom severity distributions can also alter statistical item parameters.

These are plausible considerations rather than explanations proven by the cross-sectional study. Establishing why a particular PHQ-9 item behaves differently would require additional research, potentially combining psychometric analysis with qualitative investigation of how students understand each question.

Measurement invariance supports medical versus non-medical comparisons

Measurement invariance addresses an important but frequently overlooked question: when two groups receive different questionnaire scores, are we reasonably confident that the scale is measuring the same construct in a comparable way?

The Pakistani study reported support for measurement invariance across academic discipline. This strengthens the interpretation of comparisons between medical and non-medical students because the observed group differences were not simply accompanied by clear evidence that the instrument operated fundamentally differently between the two disciplines.

This was especially relevant because non-medical students in the sample had a higher median PHQ-9 score than medical students: 10 compared with 9. In adjusted analysis, academic discipline was also associated with PHQ-9 scores. Yet the study emphasized that discipline explained only a small proportion of overall symptom variation.

Measurement invariance therefore supports the technical comparability of these groups; it does not imply that academic discipline is a major causal determinant of depression. These are separate questions.

What symptom-network findings add

The investigators also used symptom-network analysis, a method that represents symptoms as interconnected nodes rather than assuming that a total score tells the entire story.

Self-worth, concentration and downheartedness emerged among the most central symptoms in the network analysis. This overlaps with the item response theory finding that several cognitive and self-evaluative symptoms were particularly informative.

The convergence is interesting because two different analytical approaches highlighted some of the same symptoms. However, network centrality should not be interpreted as proof that targeting a particular symptom will necessarily prevent or treat depression. The study was cross-sectional, meaning symptoms were measured at one point in time. Cross-sectional associations cannot establish the temporal or causal direction of relationships among symptoms.

The reported network stability coefficients ranged from 0.31 to 0.44. Those values warrant appropriate caution when drawing strong conclusions about precise rankings of individual symptom centrality. The network findings are therefore most useful as exploratory evidence that can guide further research rather than as a clinical treatment algorithm.

Does the study prove that the PHQ-9 diagnoses depression accurately in Pakistani students?

No. This is one of the most important distinctions to preserve.

The PHQ-9 was originally designed as a brief measure of depressive symptoms and has been extensively evaluated internationally. The foundational validation work by Kroenke, Spitzer and Williams demonstrated useful criterion and construct validity in clinical populations. But diagnostic validity in a specific new population is best established by comparing questionnaire classifications against an appropriate diagnostic reference standard, such as a structured or semi-structured clinical interview.

The 602-student Pakistani study was not described as a diagnostic-accuracy study using psychiatric interviews as the reference standard. Consequently, its results provide evidence about reliability, item performance, cross-group comparability and symptom structure, but they should not be presented as a new estimate of the PHQ-9’s sensitivity or specificity for diagnosing major depressive disorder in Pakistani university students.

This distinction also explains why prevalence estimates based on screening thresholds should be described carefully. A proportion of students scoring above a PHQ-9 threshold represents the proportion screening positive or reporting symptoms above that threshold; it should not automatically be labelled the prevalence of clinically diagnosed major depressive disorder.

How should PHQ-9 scores be interpreted in university research?

The PHQ-9 produces a total score based on the frequency of nine depressive symptoms. In research, the score can be used as a continuous measure of symptom burden, categorized into conventional severity ranges, or evaluated against a prespecified screening threshold depending on the study question.

Continuous scores often preserve more information than dividing participants into positive and negative categories. They allow researchers to examine whether symptom burden changes gradually with variables such as sleep, gender or academic circumstances.

In the Pakistani study, each additional hour of sleep was associated with a lower PHQ-9 score in adjusted analysis, while female gender and a history of prior depression treatment were associated with higher scores. The association with prior depression treatment was particularly strong relative to the other predictors examined.

These findings should still be interpreted as associations. Because the study was cross-sectional, it cannot establish that changing sleep duration would produce a specific reduction in PHQ-9 score, nor can it determine whether shorter sleep preceded depressive symptoms or resulted from them.

What does the study mean for Pakistani universities?

The findings support the PHQ-9 as a practical instrument for measuring depressive symptoms in university research and potentially as one component of appropriately designed student mental-health screening programs. The evidence is particularly useful because it comes from both medical and non-medical undergraduates rather than focusing exclusively on medical students.

Several implications follow:

• University mental-health research can use the PHQ-9 with reasonable psychometric confidence. Good internal consistency and supported invariance across discipline are encouraging findings.
• Screening should not be restricted to medical students. Non-medical students in this sample reported at least comparable, and in several analyses higher, symptom levels.
• Total scores do not tell the whole story. Item response and network analyses showed that individual depressive symptoms differed in their statistical informativeness and interconnectedness.
• Screening requires a pathway for follow-up. Asking students about depressive symptoms has limited value if those with substantial symptoms or safety concerns cannot access appropriate assessment and support.
• Questionnaires should complement rather than replace clinical judgment. A PHQ-9 result is information about reported symptoms, not a standalone psychiatric diagnosis.

Important limitations when interpreting the evidence

Several limitations prevent the findings from being generalized too broadly.

First, the study was cross-sectional. Reliability and psychometric behavior can be evaluated cross-sectionally, but temporal stability and predictive validity require longitudinal evidence. Test-retest reliability, for example, asks whether scores remain appropriately stable when the underlying condition has not changed and was not established simply by calculating internal consistency.

Second, the participants were university students from Lahore. Pakistan is socially, linguistically and educationally diverse, so results from this sample should not automatically be extended to all Pakistani young adults or all universities nationwide.

Third, the study relied on self-reported questionnaires. Self-report is appropriate for instruments such as the PHQ-9, but responses can be affected by interpretation, willingness to disclose symptoms and contextual factors.

Fourth, the analyses do not substitute for a dedicated diagnostic-accuracy study. Establishing an optimal PHQ-9 threshold for identifying depressive disorders in Pakistani university students would ideally require comparison with a robust clinical reference standard.

Finally, psychometric results are properties of scores in particular contexts rather than permanent characteristics possessed by a questionnaire. Continued evaluation across languages, regions, universities and demographic groups remains valuable.

What future PHQ-9 validation research in Pakistan should examine

The 2026 study provides a useful foundation, but several research questions remain open.

1. Diagnostic accuracy

Future studies could compare the PHQ-9 with structured clinical interviews to estimate sensitivity, specificity, positive and negative predictive values, and the performance of different thresholds in Pakistani university populations.

2. Test-retest reliability

Repeated administration over an appropriate interval could help determine score stability when no meaningful clinical change is expected.

3. Responsiveness to change

Longitudinal studies could assess whether changes in PHQ-9 scores accurately reflect changes in depressive symptom burden over time.

4. Language and cultural equivalence

English, Urdu and other regional-language versions should be evaluated carefully when used in different educational groups. Translation alone does not guarantee measurement equivalence.

5. Broader measurement invariance

Future work could investigate invariance across gender, university type, language, socioeconomic groups and geographic regions. Such analyses are important when researchers intend to compare mean scores across populations.

6. Replication of item-level findings

The relatively low discrimination observed for the interest item and stronger performance of self-worth and concentration-related symptoms should be replicated independently before being treated as stable features of Pakistani student populations.

What researchers should report when using the PHQ-9

Researchers using the PHQ-9 in student studies can improve transparency by clearly reporting the version and language administered, scoring method, handling of missing responses, reliability estimate in their own sample, whether scores are analyzed continuously or categorically, and the source and rationale for any screening threshold.

If a threshold is used, terminology should distinguish a positive screen from a confirmed clinical diagnosis. Researchers comparing demographic or academic groups should also consider whether measurement invariance evidence is available or can be tested.

This approach moves psychometric reporting beyond simply citing an older validation paper. Even a well-established instrument should be evaluated within the population in which conclusions are being drawn.

Bottom line

The latest Pakistani evidence supports the PHQ-9 as a reliable and useful measure of depressive symptoms among university students. In a sample of 602 medical and non-medical undergraduates, internal consistency was good, measurement invariance across academic discipline was supported, and item-level analyses demonstrated meaningful variation in the information provided by individual symptoms.

The study therefore strengthens the evidence base for PHQ-9 use in Pakistani university research. At the same time, it demonstrates why validation should not be reduced to a single reliability coefficient. Reliability, item discrimination, cross-group equivalence, symptom relationships and diagnostic accuracy address different questions.

For universities and researchers, the practical conclusion is balanced: the PHQ-9 is a defensible brief instrument for quantifying depressive symptoms in similar student populations, but its scores require context. Screening results should not be treated as diagnoses, group differences should not automatically be interpreted causally, and individuals reporting substantial symptoms should have access to appropriate professional assessment rather than being managed on the basis of a questionnaire score alone.

Medical disclaimer: This article is for educational and research purposes only. The PHQ-9 is a symptom-screening and severity measure and cannot by itself diagnose or exclude a depressive disorder. Anyone experiencing persistent depressive symptoms, significant impairment, thoughts of self-harm or other urgent mental-health concerns should seek assessment from an appropriately qualified healthcare professional or urgent local services when necessary.