Research ethics, trials and vulnerable participants

Research ethics is the systematic study of moral principles that guide the conduct of research involving human participants. It seeks to balance the advancement of knowledge with the rights, safety, and dignity of those who contribute to studies. The core components of ethical research include informed consent, ethical review by an independent committee, and risk–benefit assessment.

Informed consent is a process whereby participants receive clear, comprehensible information about the study’s purpose, procedures, risks, benefits, and alternatives, and voluntarily agree to participate. The Declaration of Helsinki and national regulations stipulate that consent must be obtained unless a waiver is justified and approved by an ethics committee.

Ethical review is conducted by a Research Ethics Committee (REC) or Institutional Review Board (IRB). The committee evaluates the study protocol, consent documents, and recruitment strategies to ensure that the rights and welfare of participants are protected. A REC’s approval is a prerequisite for commencing a trial, except in rare circumstances where a waiver is granted. ^[2]

Risk–benefit assessment involves quantifying potential harms and benefits to participants and the broader community. This assessment guides decisions about study design, inclusion criteria, and monitoring plans.

The vulnerable population includes children, pregnant women, prisoners, individuals with cognitive impairment, and economically disadvantaged groups. These groups may have limited capacity to consent or may be at higher risk of coercion or exploitation. Ethical guidelines require additional safeguards for such participants, such as assent from children over a certain age, proxy consent from parents or guardians, and enhanced monitoring.

In cluster‑randomised trials, where groups rather than individuals are randomised, the question of who is a research subject and when consent is required becomes complex. Current guidance recommends that authors report whether ethics approval was obtained and whether informed consent was sought, including any waivers and their rationale. This transparency helps reinforce good practice and informs future regulatory guidance. ^[2]

The Declaration of Helsinki, adopted by the World Medical Association, is the cornerstone of international research ethics. It sets out principles that apply to all biomedical research involving human subjects, regardless of whether the research is clinical or basic science.

Key principles include:

1. Independent ethical review – All research studies must be reviewed and approved by an independent REC before enrolment begins.
2. Informed consent – Participants must be fully informed about the study’s aims, methods, risks, benefits, and alternatives, and must voluntarily agree to participate.
3. Risk minimisation – The potential risks to participants must be minimised and justified by the anticipated benefits.
4. Equitable selection – Participants should be selected fairly, without exploitation of vulnerable groups unless justified by the research question.

The Declaration also emphasises the importance of post‑study access to beneficial interventions and the obligation to publish results, even if they are negative.

The Declaration also provides guidance for specific populations. For example, research involving children requires parental consent and, where appropriate, assent from the child. The ability of a child under nine years to assent is limited, making parental consent essential. Recruitment in paediatric trials is often the most challenging aspect, leading to delays, increased costs, and sometimes failure to complete drug trials. Understanding parental motivations is therefore critical for advancing paediatric research. ^[4]

A multicentre trial evaluating a new stroke thrombolytic therapy enrolled 6,756 participants across nine trials. Of these, 3,391 received alteplase and 3,365 received control. Baseline data were complete for 98 % of participants, and the average age difference between the IST‑3 trial and earlier trials was 11 years, with a 20‑minute delay in treatment initiation. This example demonstrates the scale at which ethical oversight must operate and the importance of detailed reporting of participant characteristics and treatment timelines. ^[3]

Vulnerable participants require heightened ethical scrutiny. The Declaration of Helsinki and national guidelines mandate that additional safeguards be implemented to protect these groups.

In paediatric trials, informed consent is typically obtained from the parent or legal guardian. The child’s assent is sought when possible, but children under nine years have limited capacity to consent. Recruitment challenges in paediatric studies often result in delays, higher costs, and sometimes trial failure. Therefore, researchers must carefully design consent processes that respect the child’s developing autonomy while ensuring parental protection.

In cluster‑randomised trials, the unit of randomisation is a group (e.g., a hospital ward or community). Determining whether individuals within the cluster are research subjects and whether consent is required can be ambiguous. Current guidance recommends that authors report:

1. Whether ethics approval was obtained; if not, a reason must be provided.
2. Whether informed consent was sought; if a waiver was granted, the reason must be stated. ^[2]

These reporting standards aim to improve transparency, correct consent errors, and inform regulatory guidance.

Pregnant women, prisoners, and economically disadvantaged individuals also face unique ethical considerations. For instance, pregnant women may be excluded from trials to protect the fetus, but this can deny them access to potentially beneficial treatments. Ethical review must weigh the risks to both mother and child against the potential benefits.

Research ethics committees often face obstacles such as limited resources, conflicts of interest, and a focus on procedural compliance over substantive review. Auditing and accreditation can improve quality by standardising policies and promoting shared knowledge, but they may not fully capture the committees’ impact on research practices.

To evaluate the effectiveness of RECs, researchers should assess:

1. Whether REC review improves participants’ understanding of risks and benefits.
2. Whether the process influences participants’ decisions to enrol.
3. Whether it changes participants’ subjective experiences or attitudes toward research.
4. Whether it reduces the riskiness of research.
5. Whether it aligns research with local community needs.
6. Whether researchers follow REC guidance.

These metrics help determine whether the ethical review process genuinely protects participants and enhances research quality.

Research involving human participants rests on three foundational ethical principles, first articulated in the Belmont Report and now embedded in the ethical review frameworks used by research ethics committees (RECs) worldwide. These principles are respect for persons, beneficence, and justice. They are not abstract ideals but practical tools for designing, reviewing, and conducting trials that protect participants while enabling scientific progress.

Respect for persons has two core requirements. First, individuals must be treated as autonomous agents, meaning they can deliberate about their goals and act on that deliberation. In practice, this means obtaining voluntary, informed consent before enrolment. Second, persons with diminished autonomy—such as children, people with cognitive impairment, or those in dependent relationships—are entitled to protection. This is why research ethics committees scrutinise consent procedures carefully, and why trials involving older patients with cognitive decline often restrict inclusion to those at very early and mild stages of the disease. The principle also explains why investigators must report whether consent was obtained at the level of the cluster or the individual in cluster randomised trials, and whether a waiver of consent was granted by the REC, with the reason for that waiver explained. ^{[6] [2]}

Beneficence obliges researchers to maximise possible benefits and minimise possible harms. This principle underpins the ethical requirement that research be scientifically sound and that risks be proportionate to anticipated benefits. It also drives the demand for transparency in reporting: the consolidated standards of reporting trials statement provides guidance for published randomised trials, and although these standards primarily concern commercial sponsors, the principles have broad application to all clinical trials^[1]. When trials are published without disclosure of research ethics approval or informed consent, the ethical oversight process is undermined, and the scientific community cannot verify that beneficence was upheld.

Justice requires that the burdens and benefits of research be distributed fairly. This principle is violated when vulnerable populations are excluded from trials despite being major consumers of medications, as has historically been the case with older patients who account for a majority of overall medication consumption yet were rarely included in clinical trials. Justice also demands that participants recruited in clinical trials are representative of the target population. ^[6]

These three principles are operationalised through the REC review process. RECs review proposed research involving human participants, either within research institutions, as part of governmental agencies, or in the private sector. The first step in determining whether RECs are achieving their intended function is to identify what prospective research participants and their communities hope to get out of the ethics review process. This feedback loop—from principles, to review, to outcomes assessment, and back into practice—is essential for ensuring that ethical oversight is not merely bureaucratic but genuinely protective. ^[5]

In summary, the Belmont principles of respect for persons, beneficence, and justice provide the moral framework for all human research. They are translated into practice through informed consent, risk-benefit assessment, fair participant selection, and transparent reporting—each of which is monitored by research ethics committees whose effectiveness must itself be evaluated.

Research ethics committees (RECs) are central to safeguarding participants in clinical trials. Their primary objective is to assess the completeness of reporting of sample size determinations and other methodological details so that the design assumptions can be evaluated before a study commences. In a recent assessment of unpublished research protocols, it was found that most protocols lacked sufficient information to allow the sample size to be reproduced or the plausibility of the design assumptions to be assessed, highlighting a gap that RECs must address. Greater transparency in reporting sample size calculations and a stronger focus on study design during the ethical review process would allow deficiencies to be resolved early, before the trial begins. ^[1]

Guidance for RECs and the statisticians who advise them has been developed to improve the quality of sample size determinations. The quality of these determinations was evaluated in a study that aimed to create such guidance, underscoring the importance of rigorous statistical planning in the ethical review process. The study involved a systematic screening of records, with inter‑rater agreement measured by the κ statistic. Reviewers continued screening until κ reached at least 0.85, ensuring re

Methodological quality is closely linked to ethical oversight. Trials that failed to account for clustering in the design risk underestimating sample size requirements, while those that failed to account for clustering in the analysis risk overstating the statistical significance of the findings. These deficiencies were associated with a lower likelihood of reporting ethics approval. Conversely, trials that adhered to more rigorous methodological and reporting standards were more likely to report ethics approval, and articles published in journals with higher impact factors were also more likely to disclose ethics approval. This evidence suggests that robust methodological design is a marker of ethical diligence.

The global landscape of REC activity is evolving. Countries are increasingly devoting significant resources to creating or strengthening RECs, yet there has been insufficient attention to assessing whether these committees are actually improving the protection of human research participants^[1]. In low‑ and middle‑income settings, many institutions have established RECs on their own initiative, sometimes in collaboration with other countries or non‑governmental organisations, reflecting a growing recognition of the need for ethical oversight^[1]. Some countries require RECs to undergo formal accreditation. For example, in New Zealand, the Health Research Council accredits RECs, and approval by an accredited committee is necessary for researchers to access certain national databases and for participants to be eligible for compensation under the no‑fault compensation system if they suffer injuries during a study. Accreditation typically involves self‑assessment and external reviews, focusing on committee membership, operating procedures, and documentation of meetings^[1].

Finally, the impact of REC review on participants’ subjective experiences and attitudes toward research remains an area for further study. Understanding whether prospective participants comprehend the information presented to them during the consent process is essential, yet systematic assessment of participants’ understanding has not yet been fully integrated into REC oversight^[1]. Ongoing research into informed consent, capacity to consent, and the use of assessment tools in vulnerable populations continues to inform best practices for RECs worldwide.

Informed consent is the cornerstone of ethical research involving human participants. It is not merely a signed form, but a process of communication that ensures a person voluntarily agrees to participate after being adequately informed. The Declaration of Helsinki provides the foundational components: participants must be informed about the research study’s aims, procedures, potential benefits, and risks, as well as the fact that participation is voluntary. This means that consent must be given freely, without coercion, and with a genuine understanding of what participation entails. ^[2]

In practice, the reporting of consent is often inconsistent. In a review of cluster randomised trials, 69% of trials that reported consent at the individual level stated whether the method was written or verbal, whereas only 53% of trials reporting consent at the cluster level provided such details. This suggests that consent from groups or professionals may be described more loosely, sometimes merely as “agreement,” while individual patient consent is held to a higher standard. The frequency of reporting ethics approval and informed consent has increased significantly over time, although the proportion of trials obtaining patients’ consent varied widely—between 31% and 80%—depending on the intervention type. ^[2]

Cluster randomised trials pose particular challenges. No comprehensive guidelines exist for their ethical conduct and reporting. Different components of an intervention may target different kinds of participants, and each may need separate consent. Consent may be needed for randomisation, for receiving the intervention, or simply for providing data. Greater clarity is recommended in reporting whether consent was sought, from whom, and what it was for. ^[2]

Research ethics committees (RECs) sometimes spend excessive time parsing consent form wording, which can obscure larger ethical questions. Moreover, RECs rarely check whether researchers actually follow the consent processes described in their protocols—do they truly engage participants, or simply hand over a form to sign?. Simple methods such as participant feedback questionnaires or even actors posing as prospective participants could help evaluate the real consent experience.

In clinical trials, patients must understand not only the aims but also particularities such as randomisation, the use of placebos, and the possibility that they may not benefit from the treatment. Patients with mild cognitive impairment may have particular difficulty with these concepts. Consent to research is distinct from consent to treatment, and this distinction must be respected in both practice and reporting.

Vulnerable populations in clinical research include children, pregnant women, prisoners, people with cognitive impairment, those in dependent relationships (such as students or employees), and people in low-income settings where regulatory oversight may be weaker. The core ethical concern is that these groups may be recruited not because the research question genuinely requires them, but because they are easy to access or less able to refuse. This risks exploitation and undermines the principle of respect for persons.

In many low-income countries, there are no laws requiring research ethics committee (REC) oversight, or laws that exist are incomplete or under-enforced. This creates a particular vulnerability: even when research is conducted in collaboration with foreign sponsors, laws do not always require review by local RECs. Consequently, participants in these settings may be enrolled in studies without the same level of independent ethical scrutiny that would be expected elsewhere. International guidelines exist, but they are not legally binding in countries that have not chosen to adopt them. ^[5]

Cluster randomised trials raise distinct ethical issues for vulnerable groups. Because the units of random assignment are intact clusters—such as entire medical practices, hospitals, schools, or communities—individuals within those clusters may not have a meaningful choice about exposure to the intervention. This is particularly concerning when the cluster comprises vulnerable individuals, such as children in schools or patients in under-resourced hospitals, who may not have the capacity or opportunity to opt out.

Protecting vulnerable participants also requires rigorous scientific design. A study that is poorly designed—for example, with an inadequate sample size—exposes participants to risk without the prospect of producing valid knowledge. The International Conference on Harmonisation topic E9 sets down requirements for sample size reporting in protocols for drug registration studies. Trials should not be too large, as these may expose some patients to unnecessary risks. For vulnerable populations, this balance is especially critical: they should not be asked to bear risks for research that cannot yield reliable answers. ^[1]

Finally, the ethical review process itself must be accountable to vulnerable communities. Rather than assuming that REC review automatically protects participants, we should ask whether it actually reduces the number of people who, after informed consent, decide not to participate, or whether it increases the extent to which participants feel respected. For vulnerable groups, these questions are not academic—they determine whether research is conducted with them, rather than on them.

Equipoise is the ethical foundation that justifies randomising a patient in a clinical trial. It exists when there is genuine uncertainty within the expert medical community about which of two or more interventions is superior. Without this state of uncertainty, it would be unethical to assign a patient to a treatment arm by chance, because one arm would knowingly offer inferior care. Equipoise is not a static condition; it can be disturbed by emerging evidence. For example, in a meta-analysis of individual patient data from 6756 patients in nine randomised trials comparing alteplase with placebo or open control, the pre-specified analysis defined a good stroke outcome as no significant disability at 3–6 months, defined by a modified Rankin Score of 0 or 1. If such accumulating data begin to show a clear benefit for one arm, equipoise is lost and the trial should be stopped early. ^[3]

Data protection in research ethics concerns how participant information is collected, stored, and shared. Trials may use routinely available data (such as administrative or medical records) or direct intervention on or interaction with participants for purposes of data collection, including physical examination, medical tests, or interactions such as surveys or interviews. The level of data collection can be at the cluster level, the individual level, or both. Protecting these data requires clear governance. A common safeguard is the guarantor model, where one author takes responsibility for the integrity of the data and the accuracy of the data analyses. Funders should have no role in study design, data collection, data analysis, data interpretation, or writing of the report, and the corresponding author should have full access to all the data and responsibility for the decision to submit for publication. ^{[2] [3]}

Registries serve two purposes in research ethics. First, prospective trial registration (e.g., on a public registry) prevents selective reporting and duplication, and makes the existence of a trial known before results are available. Second, registries of existing data can be used to check completeness. For example, retrospective checks confirmed that no eligible trials had been omitted from a meta-analysis, including reference to a previous systematic review, an updated review of the Cochrane Stroke Group's Specialised Register of Trials, and enquiry among collaborators and the manufacturer of alteplase. Registries also help identify all relevant studies, including those with negative results, ensuring that ethical obligations to use all available evidence are met. ^[3]

Vulnerable participants are individuals whose capacity to give informed consent or to protect their own interests is diminished. This includes children, people with cognitive impairment, prisoners, pregnant women, and those in hierarchical relationships (e.g., students or employees). Research ethics committees (RECs) have a duty to protect these groups, yet the quality of their deliberations is rarely assessed. Despite the emphasis on quality assessment in other areas of health care, "there has been near silence on the possibility of applying quality assessment techniques to ethics practices". The focus has largely been on evaluating the quality of the deliberations that take place in RECs' meetings, as opposed to the impact of those deliberations on the research process itself. ^[5]

For vulnerable participants, additional safeguards are required. These may include: obtaining assent from the participant alongside proxy consent from a guardian; appointing an independent advocate; or using a data monitoring committee to oversee safety. In cluster randomised trials, vulnerability can be compounded because interventions may be delivered at the cluster level (e.g., a whole ward or community), making individual opt-out difficult. Researchers must also consider whether data collection activities themselves pose risks—for example, surveys or interviews may cause distress in vulnerable groups.

Financial conflicts of interest are particularly concerning in research involving vulnerable participants, as they may bias judgement. For example, one author has received speaker fees from and has served on the data monitoring committee of trials for Boehringer Ingelheim; his department has received research grant support from Genentech. Such interests must be declared and managed. Conversely, some researchers have not accepted fees, honoraria, or paid consultancies but are involved in clinical trials funded by Merck to the University of Oxford, with the University the trial sponsor in all cases. Transparency about funding and competing interests is essential to maintain trust, especially when participants cannot fully advocate for themselves. ^[3]

Scientific misconduct is the fabrication, falsification, or plagiarism in proposing, performing, or reviewing research, or in reporting research results. It is a fundamental betrayal of the trust that underpins the entire scientific enterprise. When researchers commit misconduct, they not only deceive their colleagues and the public, but they also risk harming patients who may be exposed to ineffective or dangerous interventions based on false data. The consequences ripple outward: resources are wasted, future studies are built on shaky foundations, and public confidence in medicine erodes.

The three classic forms of misconduct are often remembered by the mnemonic FFP:

• Fabrication – making up data or results and recording or reporting them as if they were real. This is the most blatant form of deception.
• Falsification – manipulating research materials, equipment, or processes, or changing or omitting data or results, such that the research is not accurately represented in the research record.
• Plagiarism – the appropriation of another person's ideas, processes, results, or words without giving appropriate credit, including through the unacknowledged reuse of one's own previously published work (self-plagiarism).

Beyond FFP, a broader category of questionable research practices (QRPs) exists. These include selective reporting of favourable outcomes, p-hacking (analysing data in multiple ways until a significant result emerges), and failing to disclose conflicts of interest. While QRPs may not meet the formal definition of misconduct, they are equally corrosive to scientific integrity because they are more common and often go unpunished.

The role of the REC is central to preventing misconduct before it occurs. However, a critical limitation exists: an REC's focus on structure and process cannot answer the bottom-line question of whether its review actually protects the rights and interests of research participants and their communities. For example, the fact that an REC has documented that it has considered a protocol's risks and potential benefits does not mean that it has done a good job identifying or weighing these factors. Similarly, the fact that an REC has concluded that a consent form contains all relevant information does not mean that prospective participants who read the form will actually understand or absorb the information, or that it will have any appreciable impact on their decision-making process. This gap between procedural compliance and genuine protection is a fertile ground for misconduct to take root. ^[5]

Several recurring pitfalls undermine the ethical conduct of research, and medical students should be alert to them from the very start of their careers.

Underpowered or overpowered studies. Studies that are too large or too small have been branded as unethical. An underpowered study cannot reliably answer the research question, exposing participants to risk without the prospect of producing useful knowledge. However, the view that underpowered studies are in themselves unethical has been challenged by some researchers, who argue that this is too simplistic. The correct judgement is whether a study is appropriately designed to answer the research question posed, and the validity of the sample size calculation is germane to this assessment. This is not merely a matter of whether the sample size can be recalculated, since the calculation can be correct mathematically but still be of poor quality if the assumptions used have not been suitably researched and qualified. Greater transparency in the reporting of the sample size determination and more focus on study design during the ethical review process would allow deficiencies to be resolved early, before the trial begins; once the trial starts it is too late. ^[1]

Inadequate assessment of capacity to consent. The number of clinical trials including older patients, and particularly patients with cognitive impairment, is increasing. While statutory provisions exist to make sure that the capacity to consent is assessed systematically for each patient, many gray areas remain with regard to how this assessment is made or should be made in the routine practice of clinical research. When capacity to consent for research (CR) is in doubt, it is common to consult a close relative such as the patient's support person, but the means by which this person should be designated remain unclear, and the reliability of such surrogate consent is most often questionable. ^[6]

The MacCAT-CR has limitations as a gold standard because it does not have a specific objective cut-point (clinical decision making is still required for interpretation) and was developed with reference to psychiatric expertise, which also lacks consistency. As there is currently no clear diagnostic reference to compare the reviewed diagnostic tests to, it becomes impossible to assess sensitivity and specificity of measures; this is also the main reason why the Cochrane systematic project was withdrawn from publication. Furthermore, decision-making capacity is ultimately a legal construct, which depends mainly on the external evaluation and also remains subjective, despite efforts toward standardization of procedures. ^[6]

Exploitation in international research. Research sponsors are conducting more of their studies in low and middle-income countries, both because it is less expensive and because it has become increasingly difficult to find a sufficient number of qualified participants in the sponsors' home countries. In addition, a few highly-publicized controversies have led to greater attention to the potential for exploitation in the context of international collaborative research. Low and middle-income countries are increasingly demonstrating their capacity to put into practice concrete mechanisms for enforcing ethical requirements, and international cooperation has been a key factor in this progress. However, it is not clear whether these systems have led to substantial improvements in the way that research is actually conducted. ^[5]

Ethical principles are not abstract ideals; they are operationalised daily in clinical research. Understanding where these principles are applied helps medical students see how the system is supposed to work – and where it can fail.

Research Ethics Committees (RECs) in practice. Every clinical trial involving human participants must be reviewed by an REC before it can begin. The REC scrutinises the protocol for scientific validity, risk-benefit ratio, informed consent procedures, and the fairness of participant selection. In practice, the REC's role extends beyond initial approval. A monitoring system is not an end in itself; the information generated through an assessment process must be used to stimulate improvements in practice. This requires a commitment to a process of continuous quality improvement, in which information from the assessment process is disseminated to key decision-makers and incorporated into practice. For instance, an REC might ask researchers involved in approved studies to report back about the most common questions asked by prospective participants during the informed consent process, and then use this information to change the way they evaluate informed consent forms in the future. Global or regional meetings of RECs, as well as online discussion forums, can provide valuable opportunities for sharing information and identifying and promoting best practices. ^[5]

Assessing capacity to consent in vulnerable populations. In practice, when a patient's capacity to consent for research is in doubt, clinicians and researchers must decide whether to proceed, defer, or seek surrogate consent. The MacCAT-CR is the most frequently cited existing tool, often referred to and used as a reference to assess capacity to consent to research and test the validity of other tools. Many tools have been developed using the MacCAT-CR as a reference. However, because the MacCAT-CR lacks a specific objective cut-point, clinical judgement remains essential. In practice, this means that two different assessors may reach different conclusions about the same patient, highlighting the subjectivity inherent in capacity assessment. ^[6]

International collaborative research. The increasing conduct of trials in low and middle-income countries has practical implications for ethics oversight. Local RECs in these countries are expected to review protocols with the same rigour as their counterparts in high-income countries, but they may have fewer resources and less experience. International cooperation has been a key factor in building capacity. In practice, this often involves partnerships between institutions, training programmes for REC members, and the sharing of best practices across borders. Yet the fundamental question remains: are these systems leading to substantial improvements in the way research is actually conducted? This is not merely an academic concern – it determines whether patients in these countries are genuinely protected or merely processed through a bureaucratic checklist.

Sample size and study design in practice. The debate about underpowered studies has practical consequences. When a study is being planned, the sample size calculation must be based on well-researched assumptions, not guesswork. In practice, this means that researchers must justify their expected effect sizes, standard deviations, and dropout rates with reference to prior literature or pilot data. If the assumptions are poor, the calculation may be mathematically correct but scientifically meaningless. The ethical review process should catch these problems early, before the trial begins, because once the trial starts it is too late.