Is it possible to conduct a sufficiently powered factorial experiment if I have a multilevel structure to contend with?
Yes! This is possible even when cluster randomization is necessary. For more about this see Dziak, Nahum-Shani, and Collins (2012), Nahum-Shani, Dziak, & Collins (2018), and Nahum-Shani and Dziak (2018).
Note that if one or more intervention components are group-based, there is probably a multi-level structure. This is discussed in Nahum-Shani et al. (2018).
Dziak, J. J., Nahum-Shani, I., & Collins, L. M. (2012). Multilevel factorial experiments for developing behavioral interventions: Power, sample size, and resource considerations. Psychological Methods, 17(2), 153-175.
Nahum-Shani, I., Dziak, J. J., & Collins, L. M. (2018). Multilevel factorial designs with experiment-induced clustering. Psychological Methods, 23(3), 458-479.
Nahum-Shani, I., Dziak, J. J. (2018). Multilevel factorial designs in intervention development. In Collins, L. M., & Kugler, K. C. (Eds.), Optimization of behavioral, biobehavioral, and biomedical interventions: Advanced topics. New York: Springer.
All Frequently Asked Questions
Do you see MOST intersecting with implementation science, and if so, how?
Can I expect reviewers of grant proposals to understand MOST? If not, how should I handle this in the application? There is not enough room to provide a lot of background.
I work in the prevention field, in which the horizon on the outcome is very far away. How can I optimize under these circumstances? It seems like it would take decades.
Should I apply for funding to support all three phases of MOST?
How can I find out what other studies using MOST have been conducted in my area?
How can I obtain the background I need to write a grant proposal involving MOST?
Whether you are looking for additional support as you prepare a grant proposal involving MOST or practical information helpful in managing your optimization trial, this section provides resources for a deeper dive into intervention optimization.
REDCap with Most
The goal of this manual is to show how one might setup a REDCap project to support a research study with multiple conditions, such as factorial experiments common in the Multiphase Optimization Strategy (MOST) framework.
Establishing a conceptual model and understanding optimization
Sometimes the conceptual model is not a model of a health behavior per se, but a model of maintaining treatment fidelity, promoting adherence or compliance, or the like. The conceptual model is explained in more...
Common misconceptions about factorial experiments
A factorial experiment is essentially an RCT with a lot of experimental conditions, and therefore is extremely difficult to power.
Informal introduction to factorial experimental designs
The purpose of this page is to clarify some concepts, notation, and terminology related to factorial experimental designs, and to compare and contrast factorial experiments to randomized controlled trials (RCTs). A more in-depth introduction can...
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