Good research, low costs Research into the best design for a study with a nested data structure
Dutch researcher Mirjam Moerbeek used a Veni grant to investigate how best to design a study with nested data at a reasonable cost. An examples includes an intervention study aimed at reversing unhealthy lifestyles in young people. The question is how many schools and how many pupils per school should take part.
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.
In the social sciences, experiments are often carried out in nested populations. A nested population means that people are nested in groups. It can also mean that repeated tests are carried out among people. The example of an intervention to prevent or reverse unhealthy lifestyles in young people is often carried out in schools. Here, the phrase “nested data structure” is used: the pupils are nested within schools. The results from nested data depend on the interaction between people within the same group. In the abovementioned example, results such as the smoking and drinking behaviour of pupils at the same school depend on mutual influence and communication, the school rules and the behaviour of teachers.
David Redeker | alfa
The most recent press releases about innovation >>>
Die letzten 5 Focus-News des innovations-reports im Überblick:
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Mapping the interaction of a single atom with a single photon may inform design of quantum devices
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...