Such studies have a single arm and lack a comparator arm. The only basis of deriving a conclusion from these studies is the temporal relationship of the measurements to the intervention.
However, the outcome can instead be related to other changes that occurred around the same time as the intervention, e. The change can also represent a natural variation e. Thus, the outcomes observed in such studies cannot be reliably attributed to the specific intervention, making this a weaker design than RCT.
If two or more interventions are available for a particular disease condition, the relevant question is not only whether each drug is efficacious but also whether a combination of the two is more efficacious than either of them alone. Let us think of two interventions: A and B. The participants are randomly allocated to one of four combinations of these interventions — A alone, B alone, both A and B, and neither A nor B control.
This design allows i comparison of each intervention with the control group, ii comparison of the two interventions with each other, and iii investigation of possible interactions between the two treatments whether the effect of the combination differs from the sum of effects of A and B when given separately.
As an example, in a recent study, infants in South India being administered a rotavirus vaccine were randomly assigned to receive a zinc supplement and a probiotic, only probiotic with zinc placebo , only zinc supplement with probiotic placebo , or neither probiotic placebo and zinc placebo.
This design allows the study of two interventions in the same trial without unduly increasing the required number of participants, as also the study of interaction between the two treatments. Each participant first receives one intervention usually by random allocation, as described above. Most often, the two interventions are separated by a washout period to get rid of the effect of the first intervention and to allow each participant to return to the baseline state.
For example, in a recent study, obese participants underwent two 5-day inpatient stays — with a 1-month washout period between them, during which they consumed a smoothie containing g walnuts or a macronutrient-matched placebo smoothie without nuts and underwent measurement of several blood analytes, hemodynamics, and gut microbiota.
However, this design can be used only for disease conditions which are stable and cannot be cured, and where interventions provide only transient relief. For instance, this design would be highly useful for comparing the effect of two anti-inflammatory drugs on symptoms in patients with long-standing rheumatoid arthritis. Sometimes, an intervention cannot be easily administered to individuals but can be applied to groups.
As an example, a study in Greece looked at the effect of providing meals in schools on household food security. However, such studies need a somewhat larger sample size than individual-randomized studies and the use of special statistical tools for data analysis.
National Center for Biotechnology Information , U. Shared Flashcard Set. Title Community Trials. Description Community Trials. Total Cards Subject Medical. Level Graduate. Create your own flash cards! Sign up here. Supporting users have an ad free experience! Flashcard Library Browse Search Browse.
Create Account. Additional Medical Flashcards. Term Name some of the most common forms of interventions. Definition 1. Treatment 2. Prevention 3. Behavioral: condom use. The value of randomization is as relevant when investigating community interventions as it is for studies that are directed at individuals. Randomization by group is less efficient statistically than randomization by individual, but there are reasons why randomization by group such as community may be chosen, including feasibility of delivery of the intervention, political and administrative considerations, avoiding contamination between individuals allocated to competing interventions, and the very nature of the intervention.
Evaluation of cluster-randomized trials on maternal and child health research in developing countries. Handlos, L. Masthead Jan-Feb;22 1. Respondent-driven sampling: Advantages and disadvantages from a sampling method. Methodological notes. Key concepts for searching evidence: an introduction for healthcare professionals. Processing charges. Editorial policies. Author instructions. Editorial staff. Editorial board. Willing to review? Contact and support.
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