When a red light turns to green, you can proceed ahead in your car. When your town or city turns from red to green in the Massachusetts DPH COVID-19 categories, that definitely should not be interpreted as a green light to proceed with your plans, at either an individual or local administrative level – especially now.
The current color coding scheme (from the November 12th public health report) is shown here.
These criteria came into effect Nov. 5th, and are much laxer than those used before. In the old criteria, a red designation was given to towns and cities that had a daily average of new cases per 100K over the last 2 weeks that exceeded 8. Therefore, it’s likely that some places went from red to green not because their numbers lowered, but because the criteria changed. Northampton is an example of a city that is in the green currently with a new case rate of 8.1, but that would have been in the red under the old criteria. (Update 11/20: Northampton is now in the yellow under the new criteria, with a rate of 11.0; up-to-date Northampton data can be found here).
It appears that the new criteria were adopted to be used for the Department of Education’s guidance on school reopening. They would likely be quite different if they were intended to be used in some other way, for example when deciding whether to use curbside pickup or to go into the supermarket.
Risk analyses for individual and local policy decisions involve using local new case data and positivity rates to estimate risk, and that seems to be what’s being done with this color coding scheme for school reopening decisions. As the linked articles mention, there is little consensus on what the appropriate metrics are.
Most places outside of Massachusetts seem to use county or larger regions, rather than city and town data, to make policy decisions about reopening – California uses counties, New York uses regions.
As of November 20th, Colorado will adopt a new county-based scheme that combines a new case rate, positivity rate, hospitalization numbers, testing capacity and other factors. It has 7 levels, and provides guidance for high risk populations, as well as for a range of institutions and businesses. This seems far better than what we have in Massachusetts.
To give an example of a different color-coding scheme operating at our county level, I’ve graphed Hampshire County’s new case data using Colorado’s method of relativizing to population: a two week total per 100K. Beneath the graph is the color coding scheme they use for presenting their own county data over time. Hampshire County was green in early September, blue in October, and is now orange. (Update 12/12/20: Hampshire County is now in Colorado’s red designation).