What is the appropriate level of randomization for an experimental study?

The choice of the randomization unit in an experiment is a crucial decision that impacts several aspects of the study. When opting for randomization at the individual level, where each participant receives a different treatment, there is the advantage of more precise estimates due to the reduction of intra-group variability. From another point of view, group-level randomization, where entire groups receive the same treatment, may be more efficient in terms of sampling, requiring fewer participants, the choice between these approaches must also carefully consider the study objectives, availability of resources, sensitivity to interference and the nature of the treatments in question.

The research question and design, Individual / Cluster/ Factorial randomization. The population and sampling method : Convenience sampling: If you are using a convenience sample, you may need to use stratified randomization to ensure that your groups are representative of the population. Stratified sampling: This involves dividing the population into strata based on one or more relevant characteristics, and then randomly selecting participants from each stratum. This ensures that your groups are balanced on these characteristics, even if the sample is not random. Sample size , Use the simplest level of randomization that will provide valid results / Consider the potential for bias and confounding factors

Randomization is a crucial component in experimental design, influencing the internal and external validity of the results obtained, it is a direct approach, where each experimental unit has an equal chance of being assigned to any treatment, on the other hand, stratified randomization involves dividing units into subgroups based on relevant characteristics prior to random allocation. This seeks to ensure that each stratum has adequate representation in all treatments, improving balance and representativeness. The choice between these methods depends on the specificities of the study, the characteristics of the population and the variables in question.

The choice between complete and partial randomization depends on the specific circumstances of the study, considering factors such as feasibility, ethics and research objectives. Both approaches have advantages and disadvantages, and appropriate selection will contribute to the robustness and relevance of the results obtained.

Choosing between pre- and post-randomization depends on the specific objectives of the research and considerations about the internal and external validity of the study. Pre-randomization is preferred when seeking greater control over confounding variables, while post-randomization may be more appropriate in contexts where adaptability is crucial, as long as appropriate strategies are implemented to deal with possible biases.

There are two main approaches: blind or double-blind design and open or single-blind design. In the blind or double-blind design, neither the units nor the researchers are aware of the treatment allocation. Allocation awareness can lead to inadvertent behaviors that influence results, and the choice between the two types of designs depends on the specific study objectives and ethical considerations. In general, allocation concealment is essential to ensure the credibility of the experimental design, minimizing potential sources of error and increasing confidence in the validity of the results obtained.

Always keep in mind what the purpose of your study is before deciding on a probability sample approach. If you are interested in understanding behavior of marginalized people such as career petty criminals, LGBT identifiers, etc. a probability sample is not going to be feasible. Other techniques such as theoretical sampling favored by qualitative researchers, Delphi methods etc. may be more practicable and likely to yield insights that are valuable even if the external validity of the study is compromised.