What reviewers buy next
Following reviewers across categories is the only thing this corpus can say about adjacency and substitution — and it needed the reviewer-level shuffle to say it at all.
Cross-category matrices · 54M reviewers
7 minUpdated August 2026Breadth
Most reviewers never leave one category
26.4% of reviewers only ever reviewed in a single category, and they account for 3.8% of reviews. At the other end, the 8.7% who touched ten or more categories produced 45.5% of everything. Breadth and volume are the same trait seen twice.
Reviewers and reviews by number of categories touched
Log y-axis: the distribution spans seven orders of magnitude.
Transitions
Where a reviewer goes next
Take every consecutive pair of reviews by the same person and ask whether the category changed. Kindle Store is the stickiest at 58.9% — most of the time a Kindle Store review is followed by another one. Health & Personal Care is the least sticky at 1.6%. The diagonal of the transition matrix is a measure of how self-contained a market is.
Probability the next review stays in the same category
Diagonal of the 33×33 transition matrix, as a share of that category's outgoing transitions.
Adjacency
Which shelves share readers
527 category pairs, counted by how many reviewers appear in both. The strongest link is Clothing Shoes & Jewelry ↔ Home & Kitchen with 12.9M shared reviewers. Rows and columns are ordered by total overlap, so the dense block in the top-left is the general-merchandise core that almost everyone passes through.
Shared reviewers between categories
Reviewers appearing in both categories. Log colour scale; the diagonal is omitted.
Strongest ten pairs
By absolute number of shared reviewers — which mostly means by size.
- 1Clothing Shoes & Jewelry ↔ Home & Kitchen12.9M
- 2Electronics ↔ Home & Kitchen10M
- 3Clothing Shoes & Jewelry ↔ Electronics9.5M
- 4Health & Household ↔ Home & Kitchen8.1M
- 5Home & Kitchen ↔ Tools & Home Improvement8M
- 6Clothing Shoes & Jewelry ↔ Health & Household7.6M
- 7Beauty & Personal Care ↔ Clothing Shoes & Jewelry7.2M
- 8Beauty & Personal Care ↔ Home & Kitchen7.2M
- 9Clothing Shoes & Jewelry ↔ Tools & Home Improvement7.1M
- 10Cell Phones & Accessories ↔ Home & Kitchen6.8M
Absolute overlap is dominated by the biggest categories, so this list is close to a size ranking. Turning it into a genuine affinity measure means dividing by what independence would predict — the pair counts here support that, but the published aggregates do not include the per-category reviewer totals it needs, so it is left undone rather than done wrongly.