Subject
E-commerce Data
Reading marketplace numbers — ranks, prices, ratings, listings — without mistaking them for something else.
Tutorials
- Top-N Lists Are Not the Market: Sampling Frames, Rank and Sales
A list of the 100 best sellers describes the best sellers. It is a selected sample whose members were chosen by the very thing you may want to measure. What it can and cannot tell you.
Glossary terms
- Dynamic Pricing
Changing a price frequently, often automatically, in response to demand, stock, time or competitors. One observed price is only a snapshot.
- Herfindahl–Hirschman Index (HHI)
A measure of market concentration: the sum of the squared market shares, in percent, of all sellers. It rises sharply when a few sellers dominate.
- Long Tail
The many niche items that each sell little but together make up a large share of sales, typical of markets where shelf space costs almost nothing.
- Position Bias
People click results partly because they are high on the page. Click counts therefore reflect the ranking as well as the relevance.
- Power-law Distribution
A distribution in which a few items are enormous and a long tail of items are tiny; the average is a poor summary of such data.
- Price Elasticity of Demand
How strongly the quantity bought responds to a price change: the percentage change in quantity divided by the percentage change in price.
- Product Identifier
A code that names a product so records can be matched: a seller's SKU, a global GTIN (the number under a barcode), or a marketplace's own catalogue number.
- Product Taxonomy
The hierarchy of categories a platform uses to organise products. It differs between platforms and changes over time, so a category means something only with its version.
- Product Variation
One version of a product that differs in a few attributes such as size or colour, usually grouped under a parent listing. Counts may refer to the parent or to a variant.
- Ratings and Reviews
A rating is a score a customer gives; a review is the written text. The average score reflects the people who chose to rate, not all buyers.
- Reference Price
The higher price shown beside the current price to suggest a saving. It is the seller's claim, to be stored separately from the price you pay.
- Sales Rank
A marketplace's ordering of products within a category by recent sales. It is relative, changes constantly, and is not a count of units sold.
- Search Intent
What the person behind a query is trying to achieve: find a place, learn something, or do something such as buy. Relevance depends on it.
- Seasonality
A regular pattern that repeats at a fixed period, such as higher sales every December. Without separating it, a normal seasonal rise is mistaken for growth.
- Time Series
Observations of one quantity recorded in time order. Neighbouring values are related and order matters, so time series need methods that respect time.
- Two-sided Marketplace
A platform that connects two groups, such as buyers and sellers. Its rules for listing, ranking and fees shape the numbers it publishes.