[bransonf]

It’s important to distinguish between true case burden and diagnosed case burden.

Testing is prone to variance due to behavior, test availability, development of symptoms, contact tracing effectiveness, etc... I suspect their modeling efforts use a more principled measure than positive tests.

Without even seeing the data I would infer among all tests a high positivity rate (certainly double digit).

[SpicyLemonZest]

You'd be incorrect in that inference. According to state data, the positivity rate in San Mateo County is 2.6% currently.

[bransonf]

Ah, thanks for checking. There are a few other hypotheses then:

Testing volumes are low, meaning we fail to capture a sizeable chunk of cases.

The testing strategy is bad. We’re testing people that are less likely to be positive.

And possibly, the model is just wrong.