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Debbie Duncan: Update Your Priors

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Changing times mean it's time to change. Debbie Duncan says "update your priors."

About a year ago I read an article about a term used by epidemiologists and statisticians: “Update your priors.” As I understand it, update your priors means changing your beliefs based on observed evidence. Since then I’ve watched as the pandemic became a series of updated priors.

Take masks. They were in short supply when COVID hit, so we were advised not to use them unless we were medical professionals or felt sick. I donated a box of N95s to my local hospital that I’d bought during wildfire season. Pretty quickly, though, evidence piled up showing that wearing a mask is one of the most effective means of reducing coronavirus transmission, especially indoors. Mandates followed. Yet certain Americans stuck with the no-mask advice even during those painful months and waves of deadly infections, and blamed officials for changing guidelines. Now the CDC has decreed that those who are fully vaccinated are free to ditch the mask outdoors … in most situations. Update your priors!

Last May I was afraid to touch the handle on my mailbox and constantly washed my hands. I also took my shoes off after grocery shopping, and felt guilty about not wiping down those groceries. Then scientists concluded that the primary mode of COVID transmission is airborne. Ohhh. Another update was called for when it became clear that a person didn’t have to feel sick in order to have COVID or spread it. Asymptomatic transmission? That was novel!

Updating your priors requires flexibility, an open mind and a willingness to revise beliefs as evidence warrants. It argues against making judgments that are immovable. Now when I learn more about an issue or a person that makes me feel as if I should change my mind, I say “Update your priors!”


It’s why I’m allowing my environment to become, well, a bit less sterile now that I’m fully vaccinated. It’s safe to be social! And because the outside world has lots of good bacteria that strengthen the immune system, perhaps that handle on my mailbox isn’t so scary after all.

With a Perspective, I’m Debbie Duncan.

Debbie Duncan writes children’s books from her home on the Peninsula.

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