3
$\begingroup$

I am a biology student investigating a new method of creating a dichotomous identification key. I have created a dendrogram using data I have collected from a survey on how people rate how similar pictures of plant leaves are. I used ward's method to link the clusters. In the resulting dendrogram, I have a y-axis that ranges between 0 and about 50. I know that this axis represents at which the objects are joined in a cluster, thus how far they are from other objects, but I was wondering what exactly does the numeric value represent?
enter image description here

Improve this question
$\endgroup$
2
  • $\begingroup$ Do you have a reference for this graph? $\endgroup$
    – Andy
    Jul 31, 2015 at 17:24
  • 1
    $\begingroup$ Please read the documentation for the clustering program you used. $\endgroup$
    – ttnphns
    Aug 1, 2015 at 14:57

1 Answer 1

Reset to default
2
$\begingroup$

I'm going to, ahem, go out on a limb here, ahem, and guess that you built your tree via the hclust function in base R with method = "ward.D2", which is Ward's original method. If you type ?hclust and look for height in the value (output) section, it says "The clustering height: that is, the value of the criterion associated with the clustering method for the particular agglomeration." In this case, Ward's criterion is the total within-cluster error sum of squares, which increases as you go up the tree and make the clusters bigger.

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.