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IMPORTANT The US CDC has announced that, going forward, reported SARS-CoV-2 wastewater levels will be normalized to an endemic baseline "Zero" on this baseline will be levels in the previous year @evanblake17.bsky.social @benjaminmateus.bsky.social

This does not reflect what I am reading on the CDC website. They say they are normalizing to the 10th percentile of the previous year, which is very different from what you describe. Can you point me to where you are getting your understanding?

And can you clarify what you mean by "value of the previous year"? Do you mean the median? Single day median from one year ago, or annual median from the previous 12 months? Something else?

Log transformation of the SARS-CoV-2 concentration data should produce a normal distribution (bell curve) & the selection of the 10th percentile of that bell curve should produce a baseline representing the lowest 10% values of the last 12 months of observation If I understand what they are saying

That's what I think it means as well. That is completely different from what you described in your thread.

Normalizing to a 10th percentile is not a completely unreasonable thing to do. When you're measuring things on a log scale, you need to pick a non-zero value as your baseline. The 10th percentile likely represents a conservative compromise that retains some stability in the metric.

Doesn't that depend on the shape of the normalized bell curve? Lowest 10% of these curves means very different things