5 Top Tips for Designing Your Randomised Controlled Trial

As a researcher designing a randomised controlled trial (RCT) it can be a very daunting process.  You know what you want to evaluate and roughly the population you will evaluate it with. You may have conducted your literature review on the research topic and decided on the hypothesis to be tested. You are now ready to design your own study. But where do you start? 



1. Learn from the Past

The innovation of any research question is determined by a thorough literature review. Carefully read the research for similar, prior research. Focus on the key papers published. Use the PICO (population, intervention, control, and outcomes) criteria to critically evaluate prior research in your area. Pay particular attention to the discussion section of the papers as most researchers make recommendations for future research in order to advance the area. Potential design limitations are also listed in the discussion section and can provide you with tips for design limitations that need to be addressed.     

2. Develop a Study Protocol

Writing a thorough and comprehensive study protocol document is essential, serving as a roadmap for the entire research project. A protocol developed during the planning stage allows for constructive feedback on the methodology of your study at a time when modification is possible. It is far easier to identify and correct errors in the design phase rather than adjust for them in the analysis phase. Some researchers may choose to publish their study protocol in a scientific journal. 



A study protocol should include the following:

  • Hypothesis to be tested 
  • Study rationale
  • Literature review
  • Detailed description of the study design (including population, sampling, randomisation, blinding, the proposed intervention, outcome measures, analyses) 
  • Research timeline

Check out the WHO recommendations for composing a study protocol. 

Quick Tip: make sure you include a research timeline. This can be generated in Microsoft Excel or posted on your wall to ensure you are actually following the timeline you set. 

3. Choose the Right Study Population

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Poor sampling can potentially undermine the generalisability or validity of the RCT results. Identify a target population and how you will recruit them. Establish clear inclusion and exclusion criteria appropriate to your research hypothesis. Develop a standard set of screening questions for research staff to ask during the participant recruitment phase.  

Most controlled trials are underpowered (i.e., they haven't got enough participants to detect a significant effect if there is one present). Prior to the recruitment phase, perform a sample size calculation to determine the number of participants needed. If you are not sure how, don't just not do it! Look into getting some help from a statistician or research support service.     

Quick Tip: if you are unsure what inclusion and exclusion criteria to set, take a look at previous research in your topic area and see what other researchers have specified.    

4. Develop a Study Manual of Operations 

Once you have established the study protocol and population, it is worth taking the time to develop a study-specific manual of operations for your RCT. This is a document that details how to operationalise your study protocol and conduct all study-specific procedures. In other words, the hows of  your project. Having an operations manual can help decrease the likelihood of missing data and reduce bias due to systematic differences in data collection. 

Creating research design involves seeing the project at different levels. Once you have located your project methodologically, you need to design the pacing of processes and strategies to be used, and at the same time you need to see the project as a whole.
— Thinking Research, Sage Publications
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Make sure you cover the step-by-step instructions for participant recruitment, randomisation, participant allocation, data collection methods and data entry. After developing your manual, ask yourself 'what processes have I put in place to minimise missing data at each step during the data collection phase?'  

Ensure that all research staff have read the manual. Hold training sessions to ensure all staff are trained to perform the various tasks in the standardised way. These quality control processes are essential for multi-site trials with more than one research investigator. 

5. Seek Advice from Experts 

Photo credit: Neil thomas

Photo credit: Neil thomas

It's OK to ask for advice from those who have expertise in the area. Allow a research support unit to perform the randomisation, leave the statistical analysis to a statistician, and let a health economist advise on any cost analysis. Networking with the relevant experts is invaluable in the design phase and will contribute considerably to the credence of the findings.  


A well-designed, methodologically sound RCT evaluating an intervention provides strong evidence of a cause-effect relation if one exists. It is, therefore, powerful in changing practice to promote better patient outcomes. For help with research design, study protocol documents or operation manuals email Gold Standard on research@goldstandard.com.au  

This blog is brought to you by Gold Standard Research and Consultancy. For blog recommendations email us at goldleaf@goldstandard.com.au.