No shop is the cheapest: the most frequent winner takes the lowest price in just over one comparison in ten

Zalando ES tops the list because it stocks almost everything, not because it is cheapest. It has a price in 249,804 comparisons, more than any other shop, and wins 23% of the times it competes. Futbolfactory is the opposite case: it appears about a sixth as often, but when it has a product it is the cheapest nearly half the time, 48%. Foot District (37.1%) and Sports Direct (32.9%) also win far more often than their share suggests.

Department stores and brand stores are seldom the cheapest place for what they sell. El Corte Inglés wins 15.9% of the times it competes, ABOUT YOU ES 15.5%. The official adidas store has a price in 130,944 comparisons and is the cheapest in only 14.2% of them: buying from the brand's own site is rarely the saving it looks like.

By country, Spanish shops take 57.6% of the comparisons and German shops 28.4%. That mostly reflects how many products each stocks. Head to head, a Spanish shop is the cheapest 22.8% of the times it competes, a German one 23.5% and a British one 22.3%. Buying in Spain is neither dearer nor cheaper than in Germany; the shop is what matters.

One chain does not charge the same in every country either. Zalando ES wins slightly more often than Zalando DE (23% against 21.2%). ABOUT YOU runs the other way: its German site wins 23.7% of the time, its Spanish one 15.5%. The German advantage is of little use to a shopper in Spain, though: neither Zalando DE nor ABOUT YOU DE delivers there.

The top spot keeps changing hands. Of the 15,068 products with 14 or more days of data, 78.4% changed cheapest shop at least once in the month: four in five. Vans (90.2%) and ASICS (86.5%) move most; Jordan (63.7%), Crocs (70.8%) and UGG (71.8%) are the steadiest. Behind it are reductions each shop sets on its own, and stock: when a shop sells out of its cheapest size, its price for the day goes up and another shop moves ahead.