Real-time price indices: Inflation spike and falling product variety during the Great Lockdown

We characterize inflation dynamics during the Great Lockdown using scanner data covering millions of transactions for fast-moving consumer goods in the United Kingdom. We show that there was a significant and widespread spike in inflation. First, aggregate month-to-month inflation was 2.4% in the first month of lockdown, a rate over 10 times higher than in preceding months. Over half of this increase stems from reduced frequency of promotions. Consumers' purchasing power was further eroded by a reduction in product variety. Second, 96% of households have experienced inflation in 2020, while in prior years around half of households experienced deflation. Third, there was inflation in most product categories, including those that experienced output falls. Only 13% of product categories experienced deflation, compared with over half in previous years. While market-based measures of inflation expectations point to disinflation or deflation, these findings indicate a risk of stagflation should not be ruled out. We hope our approach can serve as a template to facilitate rapid diagnosis of inflation risks during economic crises, leveraging scanner data and appropriate price indices in real-time.