White Paper » Section 6

Person Risk

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Person Risk is the chance that the other person currently has COVID. This is based on overall prevalence in your area and their recent behaviors.

So you’ve decided to meet a friend for lunch. You know the Activity Risk is 14% per hour (for an indoor unmasked lunch) and much less if you MODify your hangout. But the Activity Risk assumes that they currently have COVID.

What’s the chance that your friend actually has COVID? They aren’t coughing and they feel totally fine. Can you conclude they aren’t infected? Unfortunately, no. Roughly 55% of COVID transmissions happen when the person has no symptoms.[1]

  • Not all diseases work this way. For example, Ebola is only contagious when the person is already exhibiting symptoms. However, COVID is a different disease, and one of its defining features is that it has a high rate of transmission from people who don’t yet have symptoms.

This means that the chance someone has COVID (which we’re calling “Person Risk”) depends on their actions and choices in the past 10 days or so, not just whether they’re actively showing symptoms.

We use three different methods of guessing someone’s chance of having COVID.

  • The Basic Method is to just assume the person is “average” for their region. The chance your friend has COVID is the chance that anyone in your geographic area has COVID.
  • The Advanced Method is to add up the risk of each individual activity that person has done recently.

You do not need to understand exactly how these methods work to use the calculator, but if you want to create your own custom estimates for specific people in your life then we strongly recommend learning to use the Advanced Method and the associated risk tracking tool.

Skip ahead and takeaways

If you would like to skip ahead, please first read the following takeaways that we think are the most important things conveyed in the next few sections:

  • The chance someone has COVID is very different in different geographic regions.
    • The very same activity that is fairly safe where I live might be fairly dangerous where my parents live, because the risk that people have COVID there is higher.

If you would like to understand how we use the basic and advanced methods to calculate Person Risk, read on.

Skip ahead to Putting it all together, or read on about the Basic Method for more detail.

← Previous: Activity Risk

  1. Note that this figure includes both presymptomatic transmissions (where the person transmitting COVID will eventually show symptoms, usually within a few days, but hasn’t yet) and asymptomatic transmissions (where the person transmitting will never show symptoms). Catching COVID from someone presymptomatic is much more common: this accounts for about 50% of all transmissions, as opposed to asymptomatic transmissions which account for only about 5%. The COVID discourse tends to muddy this fact somewhat. Asymptomatic infections are inherently harder to measure (because you probably won’t get tested if you don’t show symptoms), and there are indeed plenty of them. However, most of them don’t infect anyone else. ↩︎