Hi, I am working to a new project about the correlation between acute stress and inflammatory response. The design of the study will be an RCT, and I am planning to do a stratified random allocation to match participants for age and sex. The exclusion criteria are assessed in two phases: 1. phone screening, and 2. clinical interview with a psychodiagnostic battery. I want to screen a pool of 100 candidates, from which randomising a total of 40 participants. Do I need to administer the n.2 screening phase to all participants before randomising them? Otherwise, if I randomise the participants after the phone screening, and during phase 2 a participant is excluded, is there a way to replace him without invalidating randomisation procedure?
You are getting way ahead of your self. Who do you phone and why? Define your population precisely from which a random selection will be selected. Exclusion can only occur at that stage, otherwise randomization is already flawed and biases are built in. The selection of cases is where I would focus my attention as a critic or valued. Many 'causes' of any results are found at that stage of the process. Later randomization just serves to prove what to set out to prove. Research is a waste of time and resources.
Hello dr. Kelly, thanks for your reply. The study will be a randomized clinical trial. Participants will be randomised from a cohort of voluntary, healthy students. Exclusion criteria were already established, and they include variables which could alter inflammatory and immune parameters, such as smoking cigarettes, presence of chronic diseases, or drugs use. This criteria will be assessed trough phone screening. Further exclusion criteria include the presence of psychopathology, which will be assessed during phase 2, and only if the participants resulted elegible at phase 1. I'm aware of the risks of biases during the study's design, so any help will be very useful.
My concern would be about self selection by volunteers or self exclusion. This was tried in 1930s by Gluecks using bathers on public beaches. Better to focus on a patient group needing treatment then allocate into A or B or Null. Then compare measurable outcomes.
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