The graphs above display the mean standardized revenue of companies by industry. Revenues were first standardized for every company in our sample based on the January 15 to February 25 time period, then averaged at an industry-level.
Standardized data greatly simplifies comparisons between vastly different companies and industries by showing how they are currently performing compared to their usual baseline.
This procedure takes into account both the variable’s usual mean and standard deviation. As a result, a value of 0 indicates that the current data point is equal to its historical mean, and a value of 1 that the data point is one standard deviation above the mean.
This allows us to easily see whether the current changes in revenues across an industry are within their usual bounds. In particular, the mean daily revenues displayed on the graphs can be expected to fall in the [-1, 1] range 68% of the time and in the [-1.96, 1.96] range 95% of the time. A value which falls outside the latter [-1.96, 1.96] limits can be considered a statistically significant departure from an industry’s pre-Covid-19 performance.