How Zara's $70-polka dot dress beat big data to be fashion hit of summer

It starts with Zara's army of store managers, who communicate what's selling and what trends are emerging to the commercial team within Inditex's sprawling head office

A $69.90 polka dot dress from Zara has become the fashion hit of the summer. Despite little email or social media promotion from the chain, the flowy, universally flattering mid-length frock has become so ubiquitous that someone has created an Instagram account to collect sightings of it out in the fashion wilds – including several that appear to show multiple women wearing it to the same event.

The frenzy around the garment epitomizes the ability of the brand’s parent, Inditex SA, to ride a sartorial wave.

But the company, founded by Spain’s richest man, Amancio Ortega, is coming under intensified pressure. Rivals