The elbow method helps choose K for K-means clustering. Plot the number of clusters against within-cluster sum of squares; the curve usually drops quickly, then shows diminishing returns. The bend, or elbow, suggests a practical cluster count. section 11.5.2
Use the method as a guided decision rather than an automatic answer:
- Compute within-cluster squared distances for increasing values of K. section 11.5.2
- Plot K on the x-axis and within-cluster sum of squares on the y-axis. section 11.5.2
- Look for the point where additional clusters produce noticeably smaller improvements. section 11.5.2
- Compare the result with another criterion because the elbow may be unclear or subjective. section 11.5.2
NBA payrolls and wins
For adjusted team payrolls and regular-season wins from 2000 through 2017, the elbow method suggested six clusters, while the silhouette method suggested two. The analysis chose four clusters as a compromise. The resulting K-means model isolated the New York Knicks and grouped the San Antonio Spurs with ten other teams. section 20.1




