Interpretation
Our finding that reported use of qualitative methods is rare amongst clinical registered trials is consistent with O’Cathain et al. [
22], who found that few published drug or medical device trials employed qualitative methods. Surgical trials are reputedly difficult to design and conduct, so until recently, surgeons resisted the use of randomised trials [
25]. Although the number of surgical trials being conducted is increasing [
25,
36], they face challenges; in particular the beliefs and preferences of participating surgeons threaten their equipoise, that is whether they are genuinely uncertain about the effectiveness of a clinical intervention [
37]. Many surgeons prefer not to standardise interventions, which contributes to good trial design [
38]. However, qualitative methods can describe experiences and beliefs and help in the understanding of complex phenomena. They can explore factors affecting equipoise and how to overcome these, and help to establish core outcomes and minimum standards for interventions [
7]. Hence, qualitative methods can describe surgical behaviour and explore recruitment issues in surgical trials. For example, Donovan and colleagues developed the Qualitative Recruitment Intervention [
4], which has been implemented in surgical trials [
39]. However, qualitative methods remain rare in clinical trials and research is needed to explore why.
As drug trials are better established, it is unclear why they too rarely report qualitative methods. There is evidence of the benefits of qualitative methods in drug trials, for example in understanding, identifying and addressing barriers to recruitment [
4], and exploring equipoise [
8]. As medical devices are increasing in variety and complexity [
40], there is a strong case for evaluating their benefits and harms through trials [
41]. Such trials face similar issues to surgical trials, including: when to initiate trials, when to assess outcomes, the acceptability of the intervention, the choice of outcome measures and how to implement devices into routine practice [
41]. Qualitative methods can help to tease out these issues, especially by conceptualising core outcomes [
42], showing how medical devices are perceived and integrated into existing practice [
40], and exploring the most appropriate trial design [
1]. For example, a qualitative consultation with key stakeholders, notably patients and professionals, can illuminate decisions about: trial arms, study outcomes (in particular, clinical versus patient reported) and frequency of reporting.
It is important to consider why registered trials of behavioural interventions are more likely to report using qualitative methods, as this could help to increase their use in more clinical trials. One plausible explanation is that qualitative research methods emerged from the behaviourally oriented social sciences and humanities. Such disciplines have generally avoided positivism, the dominant epistemology in biomedical sciences, in favour of interpretivism and constructionism to understand how and why people behave the way they do [
43]. Hence, using qualitative methods may be more acceptable in trials that evaluate behavioural interventions. So, advancing the use of qualitative methods in other trials may depend on convincing their researchers of the benefits of the interpretivist approach. However, this hypothesis needs careful investigation.
The continuing increase in reported use of qualitative methods in registered trials may indicate increased awareness of qualitative methods or of the potential benefits of including them in trials. Publications that may have contributed to this increase include the empirical work of O’Cathain [
1], Lewin [
3] and Flemming [
1,
3,
20] and guidance on using qualitative methods in trials [
1,
2,
22,
44,
45]. As these publications primarily addressed British trials, this may account for the greater use of qualitative methods in the UK and the UK-based ISRCTN registry.
Pragmatic randomised trials seek to evaluate interventions in normal clinical practice and thus, allow more clinical autonomy. This yields more insight into participants’ views and experiences during the trial and a more representative picture of lived experiences and real practice [
46]. Thus, more pragmatic trials are using qualitative methods to characterise patient experiences and clinical practice beyond the trial [
1,
47]. Increased adoption of pragmatic trials may also have increased the use of qualitative methods.
This review has found that, though relatively few registered trials report using qualitative methods worldwide, most of these are conducted within rich Western countries, consistent with previous reports [
3,
22]. There have been calls for more trials within poorer countries, which have a greater potential to improve public health [
48]. However, obstacles to such trials include: less capacity to deliver trials, weaker links between trial conduct and current practice, and the need to adapt trials to local context and culture. These issues make qualitative methods even more challenging [
48,
49]. Nevertheless, Vischer and colleagues [
48] have shown how qualitative methods can address these issues in low-income countries. They interviewed key informants in Burkina Faso, Ghana, Kenya and Senegal to investigate factors slowing clinical trials. Trial staff described factors apparently hindering trials, including lack of planning and poor understanding of trial processes. This generated recommendations for explicit trial planning and site organisation [
48]. Thus, qualitative methods can improve the conduct of trials in poorer countries, such as by consulting stakeholders, not least about cultural acceptability, for example of trial outcome measures. It is important, therefore, to test whether applying this approach more widely can both increase the number of trials and the proportion that use qualitative methods. It is also important to disseminate such work through publication in international journals and rigorous training.
Strengths, limitations and future directions
This review is limited to trials reported by researchers in trial registries as using qualitative methods and confirmed by inspecting their registry summaries. However, there may be registered trials that use qualitative methods without reporting this to the registry. Indeed, searching the three registries for trials using the terms ‘interviews’, ‘focus groups’ or ‘mixed methods’ identified 8267 registered trials. We checked a random 177 of these and found that 50 of their registry summaries reported the use of qualitative methods. Hence, the true number of clinical trials in these registries using qualitative methods is closer to 3800 (0.62%). This highlights two issues: Why did registries not check trials a little more thoroughly for use of qualitative components? How should registries identify trials with qualitative methods in future? We recommend that, as more trials use qualitative methods, trial registries should ask about qualitative methods within their application forms.
We did not address whether registries reported findings or whether qualitative methods influenced trial processes, outcomes or plans for implementation. With increasing pressure on trials to report findings within registries, now mandated within the US, it will soon be possible to see whether trials report qualitative findings and, in particular, whether they use qualitative methods to interpret findings or alter trial design. It will also become important to examine how registries apply those methods. Although they collect similar data, they differ in how they register trials and manage data, and above all in the proportion of trials that report the use of qualitative methods.
This review reports on important characteristics of registered trials that reported using qualitative methods, namely: when they registered, where they were conducted and the type of intervention they evaluated. Unfortunately, information was limited and inconsistent about other trial features, notably the design of the registered trials, their use of qualitative methods, their phase, sample sizes for both trials and their qualitative studies, trial outcome measures (for example, the balance between clinical and patient-reported), qualitative methods used, and how these methods related to trial objectives. While much of this information is available in the corresponding peer-reviewed publications, extracting it is a major task, as is analysing the relationship between these characteristics and trials’ use of qualitative methods.
A strength of this review is the inclusion of all trials registered between the start of 1999 and the end of 2016. This has shown a clearly increasing trajectory of trials using qualitative methods. Previous reviews covered shorter periods of time and could not analyse changes over time [
1,
3]. Including the three main international registries has improved our understanding of when and where trials are using qualitative methods.