___________ involves randomly allocating the experimental units across the treatment groups.
A randomised controlled trial with a parallel groups study design was performed. Participants were allocated to the intervention or control treatment, which they received for the entire study period. The treatment groups were followed alongside each other—hence the term parallel groups study design. The use of random allocation and the elimination of allocation bias meant that treatment groups would be similar in baseline characteristics, thereby minimising confounding. Confounding is a difference between treatment groups in the characteristics that influence the association between the treatments and outcomes. 8.1 - Randomization. In some early clinical trials, randomization was performed by constructing two balanced groups of patients and then randomly assigning the two groups to the two treatment groups. This is not always practical as most trials do not have all the patients recruited on day one of the study. In science, randomized experiments are the experiments that allow the greatest reliability and validity of statistical estimates of treatment effects. Randomization-based inference is especially important in experimental design and in survey sampling. 1 Overview. The Rubin Causal Model provides a common way to describe a randomized experiment. While the Rubin Causal Model provides a framework for defining the causal parameters (i.e., the effects of a randomized treatment on an outcome), the analysis of experiments can take a number of forms. In the above trial it was not possible to blind participants to their treatment allocation. However, allocation concealment5 was achieved by the use of an independent telephone randomisation service not involved with recruitment, clinical care, or assessment of the outcomes. In the statistical theory of design of experiments, randomization involves randomly allocating the experimental units across the treatment groups. Treatment allocation in a clinical trial can be randomized or nonrandomized. Nonrandomized schemes, such as investigator-selected treatment assignments, are susceptible to large biases. Even nonrandomized schemes that are systematic, such as alternating treatments, are susceptible to discovery and could lead to bias. For example, consider a two-armed trial with a target sample size of 96 randomized subjects (48 within each treatment group). The pharmacist constructs 96 drug packets and randomly assigns numeric codes from 01 to 96 which are printed on the drug packet labels. Randomization in permuted blocks is one approach to achieve balance across treatment groups. The randomization scheme consists of a sequence of blocks such that each block contains a pre-specified number of treatment assignments in random order.
Randomization