groups » Global Health Research Process Map » Study population, sample size and statistics

Study population, sample size and statistics

It is very important to identify your study population and the sample size required at an early stage. The sample size will depend on the trial design that is appropriate for your study and will be governed by your chosen power requirements and any statistical tests that you are planning to use. You also need to consider if recruitment in your study population is feasible; what is the incidence of the disease you are studying, how strict is your exclusion criteria and will the population volunteer? These questions have important implications for deciding if recruitment is possible and how long it will take. The longer the trial takes to recruit participants, the costlier the trial will become.
Useful resources:

1. The Trial Protocol Tool has a very useful sections on population, sample size, analysis strategies and statistical considerations:

Articles on study design and statistics for beginners:

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Please use the comment box to explain any problems that you have with this process step or any solutions that you have found to make this step easier for others. If you have any suggestions for additional resources or guidance, please provide these below.

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  • thuy thuy 27 Jun 2011

    I would like to add some common terms using in Clinical trials.

    Concept related to consent but not consistently defined. In UK, where a prospective trial participant is unable to give informed consent to participate, a legal representative may give assent on his/her behalf. In USA, however, assent is used for the agreement of the person who is unable to give consent.
    Subject/ Participant
    Defined in the ICH guideline E6 as ‘An individual who participates in a clinical trial, either as a recipient of the investigational product(s) or as a control.’
    Regulator/ Regulatory Authorities
    Bodies having the power to regulate. In the ICH GCP guideline the expression Regulatory Authorities includes the authorities that review submitted clinical data and those that conduct inspections. These bodies are sometimes referred to as competent authorities.


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