The ONLY distinguishing feature of a RCT is that 2 or more groups are formed by random allocation. Other things, blinding, theoretical justification for intervention, baseline tests may be important but are not sufficient for a study to be a RCT.
Avoid selection bias
Controls for temporal effects
Controls for regression to the mean
Basis for statistical inference
Simple Randomisation:
Each participant has an equal chance of being assigned to any group, often using random number generators or computer algorithms
Stratified Randomisation:
Participants are divided into subgroups (strata) based on specific characteristics (e.g., age, gender). Randomisation occurs within each stratum to ensure balanced groups
Paired Randomisation:
Participants are matched in pairs based on certain criteria (e.g., age, baseline measurements). Each pair is then randomly assigned to different groups
Pairwise Randomisation:
Similar to paired randomisation, but focuses on creating pairs of treatments rather than participants. Each pair of treatments is randomly assigned to participants
Minimisation:
Not true randomisation. The first participant is randomly assigned, and subsequent assignments aim to minimise imbalance in predefined characteristics across groups. It uses a weighted probability to achieve balance[3].
Block Randomisation:
Ensures that groups are balanced in size by dividing participants into blocks and then randomly assigning them within each block
Cluster Randomisation:
Instead of individual participants, groups or clusters (e.g., schools, clinics) are randomly assigned to different interventions
Adaptive Randomisation:
Adjusts the randomisation probabilities based on accumulating data to improve the balance of participant characteristics across groups
There are 3 groups. These include:
Participants
Researcher delivering the intervention
Researcher / Assessor measuring Pre and Post intervention
NB Simply Single is where any one of these is blinded, double is where any two and simply triple is any three.
Further Reading: This article explain the complexity of understanding blinding.