A category called "Running Shoes" promises a choice. If the first three rows are one brand, the page keeps a different promise: it has become that brand's page under another name. Visitors who came to compare do not find a comparison, and the other brands you stock might as well not be there.
How it happens
Nobody decides to give a category to one brand. It follows from sorting by performance.
A strong brand sells well. Its products rank high. High positions bring views, views bring sales, and sales confirm the positions. Each product earns its place fairly, and the sum is a page with one logo on it. The better your sorting follows sales, the more it tends this way.
The assortment can add to it. If one brand supplies half the products in a category, even a random order would show it everywhere.
Measure it
The simple measure is the share of the collection that belongs to its largest brand. Count the products of each brand, take the biggest count, divide by the number of products.
Two cases should be left out:
- Brand collections. A brand page has one brand by design.
- Small collections. With ten products there is nothing meaningful to say about variety.
This is the Product Diversity signal of Merchandiser's Collection Health Score. It names the largest brand and its share of the assortment, skips brand pages and small collections, and lowers the collection's score as that share grows. The recommendation that comes with it is to cap repetition from a single brand to keep the shelf varied.
Merchandiser reports this; it does not enforce it. It will not hold back a product because the brand already has three in the row. What to do with the finding is your decision, and the options are below.
Look at the first rows too
The share across the whole collection is the stable number. What the visitor experiences is the first screen. A brand with a fifth of the assortment can still fill the first row if its products are the top five performers.
So when the signal flags a collection, open the sort page and look at the top. In Merchandiser the sort page can be set to the same number of products per row as your storefront, which shows the page as customers see it.
What to do about it
Start with the assortment. If one brand is most of the category, the page is telling the truth about what you stock. Sorting cannot create variety that is not there. Either widen the range or accept that this category is effectively a brand page.
Then look at the rule. A sorting rule can use brand as an attribute. A rule can give the other brands of a category a modest lift, or the dominant brand a modest reduction, so that the order still follows performance and the first rows mix. Keep the adjustment small: the goal is a page that offers a choice, not one that hides what sells.
Use pins for the first row, sparingly. Pinning one strong product of a second and a third brand into the first row guarantees variety where it matters most. This is curation, and it needs the upkeep pins always need; see Pinned Products: When to Pin and When to Let Go.
Split the category. If customers think in brands in this category, give them brand pages and let the mixed page be the overview.
When dominance is fine
Variety is not a goal in itself. Some categories are one brand's territory, and customers come for that brand. If the dominant brand is what people search for and buy, forcing others into the first row costs sales.
The signal is a prompt to look, and the test is the customer's intention. Did they come to choose between brands? Then show them a choice. Did they come for the brand? Then the page is doing its job.
Where it fits
Brand diversity is one of seven signals of a category page's condition. The others, including availability at the top of the page and the freshness of the sort, are covered in What a Healthy Category Page Looks Like.