Wat is Alternative data, panel drift?

Alternative data are data about companies, economies or markets from sources other than prices, filings and official statistics: card and bank transactions, receipts, web traffic and prices, app usage, geolocation, satellite and aerial images, shipping and flight records, job postings, text. A dataset built on a panel (of cardholders, devices, stores) suffers panel drift when the panel’s composition or its relation to the quantity it measures changes over time: a provider change, attrition, a new source, a re-weighting.