How to design my study?

Study Population

What should I do first when trying to determine my study population?

We want to make sure you are set up for success with a feasible and large enough recruitment pool. This document may help you think through your study sample, sampling method, and sample size.

How do I determine my inclusion and exclusion criteria?

Carefully describing your study population through inclusion and exclusion criteria increases the chances that your results will be reliable and reproducible.

  • What are the characteristics of participants needed for your study? Consider the variables you wish to include in your study. It may help to think through inclusion criteria first; inclusion criteria may be thought of as a potential subject’s ticket through the door for consideration in your study (common factors: age, gender, stage of disease, etc). Next, think through any factors that would disqualify participants from being a good fit for your study (e.g. comorbidities, current medications etc.).
  • The IT data analysis form, which you complete to obtain data, requires specifics on the population within the EMR or data registry.

Where can I find my study population? 

You may want to use already collected data for your study (e.g. from the EMR at CMHS). Alternatively, you may need to go straight to the source – the participants themselves – and recruit subjects. GME Research Staff can connect you with CMHS data on your proposed study population and support you through this decision.

What should I do if my study population is too small? 

If you are worried that your sample will be too small, consider:

  • Broadening the variable categories you have applied to your study population (such as a wider age range)
  • Determining whether you can remove an exclusion criterion or comorbidity to analyze separately while still maintaining the integrity of the research question, scope of the project, and the scientific value
  • Expanding the study population to nearby hospitals through a proxy IRB process
  • Utilizing data from national databases


What if I don’t directly care for the patients who would be enrolled in my prospective study? 

If you do not have access to the study population, you need to figure out who will collaborate with you on your study idea. Consider what would be required of that potential collaborator and what they would get from collaboration. In line with the level of involvement, research team members should be listed as co-investigators.

What should I consider when designing my recruitment plan? 

  • Conceptually, your recruitment plan will need to be non-coercive, voluntary, and respectful.
  • Logistically, think through: when, where, and how you will approach potential participants. Consider if your recruitment site location is appropriate – both in terms of logistics as well as whether or not the potential participant would have enough time and capacity to participate. 
  • To make sure that participants have all the information they need to decide whether or not to participate, make sure that the approach occurs in an appropriate setting: consider where potential participants are at the time that they might consent to participate in your study. Do patients have the medical decision making capacity to process the opportunity fully and provide fully informed consent?
    • Ex: it would not be appropriate to attempt to recruit or consent a patient if they were in acute and overwhelming pain or impaired.
  • The IRB must approve all recruitment materials, such as scripts, emails, or printed/electronic materials used to recruit participants.
    • Pro Tip: be sure to use plain and clear language when communicating with a potential participant during the recruitment and consenting process. A great resource can be this glossary that allows you to look up lay language for medical terms.

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