• An increasing number of new cases is not necessarily cause for alarm. See "growth in new cases" below.

• A growth rate of 20% means new cases double about every 4 days.
• A growth rate of 30% means new cases double in less than 3 days.
• An upward slope is highly problematic:
  • This is the worst case.
  • The spread of the virus is largely unchecked.
• A horizontal slope (above 0%) is still problematic:
  • This will still lead to, over time, exponential increases in new cases
• A downward slope is encouraging:
  • The rate of new case creation is diminishing, but not the number of new cases until the line dips below 0%

Change in growth of new cases (4 day moving average of new case growth) (added on 3/26 for Europe, US, Americas)

• The change in the change of new cases.
• This is the second derivative of new case growth.
• Below 0 means decelerating new cases; Above 0 means accelerating new cases

• There is little interpretation here. The data is derived from the growth in new cases (see above)
• Obviously, this is a theoretical number of days. More densely populated urban areas will be impacted more quickly than sparsely populated rural areas. Recent preventative measures (such as shelter-in-place) may substantially impact the horizon.

• Thomas Pueyo (March 10, 2020) provides analysis of why quick action (e.g., social distancing) is so important.

• Columbia University US model (March 20, 2020) also illustrates the impact of social distancing and other countermeasures.

• Imperial College (UK) model (March 16, 2020) also illustrates the impact of social distancing and other countermeasures. Their model shows cases for the UK (with no intervention) peaking prior to April 20 and largely complete by June. Our simple model is in line with this more refined model.