In the design phase of an intervention study, the first issue to be decided is how to assign people to different experimental groups. There are two groups in studies such as the model example above: the intervention group and the control group. One option is to assign whole schools to a particular group, so that all pupils from the same school experience the same conditions. Another option is to assign the pupils from each school to different groups so that each group is represented at each school.
The sample size needs to be determined in the next phase. This should be designed in such a fashion that any difference between the groups has the greatest possible chance of being identified. In the model, the question is whether many schools should be included and a small sample taken from each, or just a few schools with a large sample taken from each. From Moerbeek’s research it can be concluded that a trial using many small schools is preferable, if the costs at school level are relatively low and the degree of mutual influence between pupils within the same school is high.
This research was conducted because a few years ago little was known about the number of people in trials using nested data. Using too few people usually means that the effect of an intervention cannot be demonstrated on the basis of statistical data analyses, whereas the inclusion of too many people means unnecessarily high costs. The results of this research will contribute to the improved design of trials using nested data, which will enable trials to produce good results against reasonable costs.Nested populations
David Redeker | alfa
Illinois researchers researchers find tweeting in cities lower than expected
21.02.2018 | University of Illinois College of Engineering
Polluted air may pollute our morality
08.02.2018 | Association for Psychological Science
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
20.04.2018 | Physics and Astronomy
20.04.2018 | Interdisciplinary Research
20.04.2018 | Physics and Astronomy