Why are research study criteria so strict or specific?

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Category: Useful Information
Published on Thursday, 29 May 2025 17:31
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We will promote research about fibromyalgia as often as we can. This research comes from various institutions and involves students and academics at different levels. Different research will have varying requirements that change depending on what type of study, what level it is at and the type of research it is conducting. Some examples on the types of study and how they can vary is listed below:
  • Undergraduates are learning their subject and finding out how to research a subject. These studies will typically feature a very limited scope, require very few participants i.e. under 10 and the student will appreciate feedback on the methods as well as the study itself.
  • MSC / Postgraduate are further on than Undergraduates, but they are still more focussed on learning about their subject than adding to new fibromyalgia knowledge. These studies will still require small numbers of respondents.
  • Funded or PhD research is more what we would consider “proper” fibromyalgia research, with the researchers aiming to increase their knowledge but also add new information to their field of study. The number of participants for these studies can vary widely, from 15 to 300 and beyond. 
With this in mind, the criteria for who is to be included and who is not will vary significantly. An undergraduate may be looking for 10 people with fibromyalgia, but a PhD researcher may be looking for 50 women who have fibro along with current in part-time or full-time employment and have children. The more involved or complicated the research is will tend to mean that the inclusion and exclusion criteria is more specific.  
 
However, people often in our communities why the research criteria are often specific in certain requirements. This may be because they want to take part and feel excluded or underrepresented. Common examples are:
  • Why is there an age requirement, e.g. over 40s?
  • Why do they only want women?
  • Why do they not want people with this condition? e.g. fibromyalgia and polymyalgia
  • Why are they excluding people with MS?

Reasons for having specific inclusion criteria

In a clinical research study, the inclusion criteria are critical for several reasons, and their strictness is essential to ensure the integrity and validity of the study. Here are the key reasons why inclusion criteria are important:
  1. Homogeneity of the Study Population
    • Consistency: Strict inclusion criteria help create a more homogeneous study population, which reduces variability in the responses to the intervention being tested. This consistency allows researchers to better isolate the effects of the treatment or intervention.
      Target Population: By defining specific characteristics (e.g., age, gender, disease stage), researchers can ensure that the study population closely resembles the target population for whom the treatment is intended.
    • Safety and Ethical Considerations:
  2. Minimizing Risk
    • Inclusion criteria help identify individuals who are most likely to benefit from the intervention and least likely to experience adverse effects. This is particularly important in studies involving new or experimental treatments.
    • Protecting Vulnerable Populations: Strict criteria can help protect vulnerable populations from being exposed to potentially harmful interventions.
  3. Scientific Validity
    • Clear Outcomes: By selecting participants with specific characteristics, researchers can more accurately measure the outcomes of interest. This clarity is essential for drawing valid conclusions from the study.
    • Generalizability: While strict inclusion criteria may limit the generalizability of the findings, they ensure that the results are applicable to a well-defined group, which can be critical for understanding the treatment's effects.4. Regulatory Compliance:
  4. Adherence to Guidelines
    • Regulatory bodies often require strict inclusion criteria to ensure that studies are conducted ethically and scientifically. Compliance with these guidelines is essential for the approval of new treatments.
  5. Facilitating Recruitment and Retention
    • Targeted Recruitment: Clear and strict inclusion criteria help researchers identify and recruit suitable participants more effectively. This targeted approach can streamline the recruitment process and improve retention rates throughout the study.
  6. Data Integrity:
    • Reducing Confounding Variables: By limiting the study population to those who meet specific criteria, researchers can reduce the influence of confounding variables that could skew the results. This enhances the reliability of the data collected.
A real world example from a study where males were difficult to recruit onto a study and the lack of male participants interferes with the statistical power and data interpretation. The study recruited over 900 participants with fewer than 40 males being included, and this results in a significant imbalance that would be challenging to account for confounding factors. Thus, the tendency is to start with a female only cohort to limit variability and once proof of purpose has been established attempt to expand to males.
 
The purpose of research studies is not to cover everyone but to prove that some intervention or change in practice is safe firstly, then effective, and then it can hopefully be expanded to wider groups beyond the study cohort. Keeping confounding factors to a minimum helps with cost, design and the overall effectiveness and robustness of the study.

Conclusion

In summary, strict inclusion criteria in clinical research studies are essential for ensuring the safety of participants, maintaining the scientific validity of the study, and facilitating regulatory compliance. While they may limit the generalisability of the findings, they are crucial for producing reliable and interpretable results that can inform clinical practice and future research.
 

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