**Let’s throw some math at the question…**

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It’s not a conscious thing, but these days, our brains are constantly running risk assessments:

- What’s the likelihood that I get exposed to COVID?
- What’s the likelihood that I get infected?
- How bad will it be if I do get infected?

Unfortunately, “the science” hasn’t been providing us with much useful “data to follow” on those questions.

So far, the best data is on question #3: How bad will it be if I do get infected?

#### CDC: 95% survivability rate if over 70 … higher with no symptoms, no co-morbidities or younger.

Those are pretty good odds, right?

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Today, let’s look at question #1 — **the likelihood of getting exposed to the virus**, say, at a Thanksgiving gathering.

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To start, let’s “reframe” the question and ask **What’s the probability that at least one person at the gathering is infected?**

The pivotal base case data variable is what’s called the “**prevalence rate**” — the percentage of people in the relevant population who are currently infected.

The best guesstimate that I’ve found is that the national prevalence rate is between 1% and 3% … most likely about 2%.

Let’s work with the 2% number and, for simplicity, assume that we have a T-Day gathering of 5 people drawn randomly from the national population.

What’s the likelihood that at least 1 member of the group is currently infected (and presumed contagious)?

Again, we have to reframe the question and ask: **What’s the probability that none of the 5 are infected?**

If there’s a 2% chance that a person is infected, there’s a 98% chance that they’re not infected.

So, for a 5-person group, the probability of __no one__ being infected is a “chain probability”: 98% raised to the 5th power — 98% x 98% x 98% x 98% x 98% = 90.4%.

That means that there’s a 9.6% chance that at least one person is infected (100% – 90.4% – 9.6%) … and, possibly contagious.

Got it?

Let’s expand across the prevalence rate range and vary the group sizes:

For example, if you’re drawing a group of 10 from a high prevalence population, then there’s a 1 in 4 chance (**26.3%** to be precise) that at least 1 person in the group is infected.

**Is that a risk worth taking?**

Maybe yes, maybe no.

**Having a possibly infected person at your party doesn’t necessarily mean that you’ll get infected.**

**It depends on your immune system, the infected person’s contagion severity, and the nature of your exposure.**

For example, **your risk is higher if**:

- You’re in the vulnerable class: old with co-morbidities
- The infected person is drawn from a higher prevalence population, e.g. a known hot spot locale
*(think: spiking city or college campus)* - The infected person is highly contagious
*(i.e. studies indicate that a symptomatic infectee is 2 or 3 times more contagious than an asymptomatic infectee)* - You are in prolonged close contact with the infectee
- Nobody is wearing a mask

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So, the way I’m thinking about the risk:

**Stay away to protect yourself if you’re vulnerable.**

**Stay away to protect others if:**

- You’re symptomatic
- You work or play in a COVID-hostile environment
- You’re a unbridled hugger, kisser or close talker

Otherwise, given the survivability numbers, I’m willing to take the risk.

Happy Thanksgiving!

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