Dendograms and its interpretation
A dendrogram is a tree diagram frequently used to
illustrate the arrangement of the clusters produced by hierarchical clustering.
Dendrograms are often used in computational biology to illustrate the clustering
of genes or samples.
Dendrograms are a convenient way of depicting
pair-wise dissimilarity between objects, commonly associated with the topic of
cluster analysis. This is a complex subject that is best left to experts and
textbooks, so I won't even attempt to cover it here. I have been frequently
using dendrograms as part of my investigations into dissimilarity computed
between soil profiles. Unfortunately the interpretation of dendrograms is not
very intuitive, especially when the source data are complex. In addition,
pair-wise dissimimlarity computed between soil profiles and visualized via
dendrogram should not be confused with the use of dendrograms in the field of
cladistics-- where relation to a common ancestor is depicted.
An example is presented below that illustrates the
relationship between dendrogram and dissimilarity as evaluated between objects
with 2 variables. Essentially, the level at which branches merge (relative to
the "root" of the tree) is related to their similarity. In the
example below it is clear that (in terms of clay and rock fragment content)
soils 4 and 5 are more similar to each other than to soil 2. In addition, soils
1 and 3 are more similar to each other than soils 4 and 5 are to soil 2. Recall
that in this case pair-wise dissimilarity is based on the Euclidean distance
between soils in terms of their clay content and rock fragment content.
Therefore proximity in the scatter plot of frock frags vs. clay is directly
related to our simple evaluation of "dissimilarity".
A detailed information is given in the following
link: