We found no substantial effect of screening or case-finding instruments on the overall recognition rates of depression, the management of depression by clinicians or on depression outcomes. These findings were true for both primary care and general hospital settings.
The finding that routinely administered screening or case-finding instruments for depression have little impact on the recognition of depression is a robust finding based on several large-scale studies. In a subset of studies that used the more complex 2-stage screening and feedback methods, there was some evidence of improved recognition. A further finding from our exploration of between-study heterogeneity is that depression-specific instruments seem to influence clinicians to a greater extent than less specific instruments, such as the General Health Questionnaire, that measure both depression and anxiety. It would seem that when information is specific and requires little additional computation on the part of the clinician, they may more readily integrate this information into their clinical decision-making process. Our finding that high-risk screening strategies might be more effective than unselected strategies might reflect an implicit decision-making process among clinicians, whereby they are more likely to act on the basis of information when there is strong positive likelihood that the information predicts the presence of a disorder. Among previously unselected patients, the prevalence of depression will be low (< 10%) and the post-test probability will be less than 50%, meaning that a positive screening test will be wrong more often than it is right. In this sense, our findings may reflect the Bayesian processes inherent in many clinical decisions.41
These are areas that deserve further research and may point the way to finding an effective role for screening instruments in nonspecialist settings.
Despite our best efforts in summarizing these data, there are several limitations largely related to the primary studies included. First, most studies did not report adequate concealment of allocation or the method of randomization; thus, we could not determine the susceptibility to bias.42
Second, we were unable to account for some of the substantial heterogeneity that remained between studies. Further research should seek to identify other sources of clinical heterogeneity. Lastly, we should urge caution in drawing firm conclusions from any suggestive findings based upon our exploratory meta-regression analysis, since this involves making observational comparisons within randomized studies and the power of causal inference is therefore reduced.21
These results should be considered hypothesis generating and further randomized trials are needed to test the robustness of these findings.
Previously, researchers have sought to apply systematic review methods to establish the effectiveness of screening for depression,8,9
but with seemingly contradictory results.43
The results presented in this review should be considered alongside those of a 2002 report by the US Preventive Services Task Force9
and an updated reported by the Canadian Task Force on Preventive Health Care based on the US review.4
An Australian “review of reviews” by Hickie and colleagues in 2002 placed great emphasis on the results of the review by the US Preventive Services Task Force, but they did not include subsequent research or reviews included in our review.43
Thus, to explore the reasons for this apparent divergence in results, we need to compare our methods and results with those of the US Preventive Services Task Force review.9
We believe our findings are largely consistent with the reviews by the US Preventive Services Task Force and the Canadian Task Force on Preventive Health Care; however, the following differences should be noted. First, our review updates the reviews by the US Preventive Services Task Force and the Canadian Task Force on Preventive Health Care, and it includes 3 studies were published after the other 2 reviews24,26,35
and 3 studies that were not included in the US Preventive Services Task Force review.28,29,36
Second, although the results were broadly similar in both settings, our review focuses on screening in any setting, compared with the reviews by the US Preventive Services Task Force and Canadian Task Force on Preventive Health Care, which focused on primary care alone. Third, we excluded 1 study that had been included in both the US Preventive Services Task Force and Canadian Task Force on Preventive Health Care reviews because it did not meet our inclusion criteria.44
The most notable difference is that our review focuses on screening strategies alone and does not include studies in which screening was embedded within wider enhanced-care programs. The results of our review are, therefore, only relevant to stand-alone screening programs, for which we found clear evidence of limited or no benefit. The set of interventions reviewed by US Preventive Services Task Force and Canadian Task Force on Preventive Health Care included those in which screening was included as a part of enhanced patient care and clinician support (collaborative care and quality-improvement strategies).45–47
Of particular importance was the inclusion of a large US study, the Partners in Care study,47
whose results were strongly in favour of the active intervention (screening with collaborative care), which included face-to-face clinician education; computerized decision support; individualized treatment algorithms; psychotherapy or drug treatment; active support by a case manager; and regular consultation with a specialized mental health clinician (psychologist or psychiatrist). This study accounted for between 30% and 47% of the weighted information in the meta-analyses produced by the US Preventive Services Task Force.9
Complex enhanced collaborative care for depression improves the outcomes of depression, and these packages have been comprehensively reviewed elsewhere.10,13,48
We do not question the effectiveness of these strategies, but it remains unclear whether screening is a necessary component of enhanced collaborative care for depression. From a recent review of the necessary components of collaborative care,10
several other factors emerged as potentially necessary (and statistically significant) components including the use of coordinated patient follow-up, case managers with a mental health background and regular supervision of case managers.10
Thus, the previous reviews by the US Preventive Services Task Force and Canadian Task Force on Preventive Health Care, which mixed studies of enhanced care (some including screening) and screening alone, do not provide reliable evidence on the effectiveness of screening. Many studies that include complex enhancements of care have not used screening as a recruitment strategy, but they have also reported positive results.49–51
Further trials in this area should compare the relative effectiveness of enhancements of care with and without screening.
Our review complements those by the US Preventive Services Task Force and Canadian Task Force on Preventive Health Care, and it enhances our understanding of prior work and the available and more recent evidence. It helps us to better understand the role of screening in general and confirms that screening without other systematic changes to improve depression management is unlikely to improve outcomes. This is of particular importance to policy makers who may have ignored the key recommendations of the US Preventive Services Task Force and Canadian Task Force on Preventive Health Care in the provision of additional management strategies for depression. In practice, screening strategies have often either been recommended for populations at high risk for depression, such as those with chronic illness, or adopted alone and without further enhancements of care.7
@ See related article page 1023