What is Nested Design
Nested design is a design in which levels of one factor are hierarchically subsumed under (or nested within) levels of another factor.
The general idea of nesting refers to situations where subdivisions (levels) of a given factor change for the various subdivisions of the other factors.
It means a design where experiments have several factors whose levels are nested within the levels of the other factors.
Examples of Nested Design
Suppose a drinking water supply organization is interested in studying the chlorine content of water in 3 major districts. 8 villages will be selected at random within each district and 50 households will be selected at random within each selected village for measuring the chlorine content.
Here, there are 3 factors; districts, villages, and households.
The major factor is districts and probably is fixed; the other 2 factors are nested: villages within districts and households within villages.
The nested factors would be assumed to exhibit random effects, most likely.
Generally, the major factor or first stage is assumed to be fixed while the nested factors are assumed to be random.
Example of Nested Design in Forest Inventory
Forest carbon measurement can be carried out in both rectangular and circular plots.
Nevertheless, circular samples are recommended for the study because they are relatively easy to establish.
As discussed previously, the radius of each plot is dependent on the density of the forest, the default being an 8.92 m radius for moderately dense vegetation. As illustrated in Figure.
Several subplots are established within each plot inside of the 8.92 m radius plot, a subplot with a 5.64 m is established for saplings; a sub-plot with a 1 m radius is established for counting regeneration; and a subplot with a 0.56 m radius is established for sampling leaf litter, herbs, grass, and soil.