A data scientist runs PROC CLUSTER with METHOD=AVERAGE (unweighted average linkage) and then uses PROC TREE to create cluster assignments. What does average linkage use to compute the distance between two clusters?
Select an answer to reveal the explanation.
Short Explanation
Here's the deal — average linkage uses the average of all pairwise distances between points in the two clusters. That's UPGMA, and it's what you're relying on when PROC CLUSTER uses METHOD=AVERAGE before PROC TREE assigns clusters.
Full Explanation
Average linkage (UPGMA — Unweighted Pair Group Method with Arithmetic Mean) defines cluster distance as the average of all pairwise distances between members of the two clusters. The closest-points description is single linkage (nearest neighbor). The centroid-distance description is centroid linkage. The farthest-points description is complete linkage (farthest neighbor).