Talk:positivity rate

This definition really needs to be clarified as the term is in common use with regard to Covid-19 and other viral infections, and the definition is not clear. There appears to be a lot of confusion and it is of vital importance that everyone understands the terminology.

The current definition says "The percentage of people who have tested positive out of all of those who have been tested (for a given pathogen)". This means the prevalence of people who have tested positive assuming a large enough sample to be statistically significant.

The problem for Covid-19 and presumably other viruses is that there are two VERY different types of tests for Covid-19 to which one might test positive. One type shows whether the person has a currently active case of Covid and is therefore likely contagious. The other type of test shows if the person has had a Covid infection in the past (possibly with no symptoms), by testing the person's antibodies against the virus, and is therefore likely immune.

I suspect that positivity rate is supposed to mean the percentage that currently have an active infection. I have however seen the word used both ways because it is largely misused and misunderstood and causes confusion at a time when understanding is crucial.

This page "https://coronavirus.jhu.edu/testing/differences-in-positivity-rates" from Johns Hopkins (one of the acknowledged expert sources of information for Covid-19) says, in the second paragraph: "test positivity is a measure of testing capacity and while it can provide important context about case totals and trends, it is NOT a measure of how prevalent the virus is in communities". This seems to imply that positivity rate is the percentage of positive tests compared to the number of people that COULD be tested and is therefore not the prevalence in the community which the Wiki definition implies. Also the 1st bullet point discusses the problem that I outlined above with two very different types of tests that one could test positive for.

This page https://www.fda.gov/consumers/consumer-updates/coronavirus-disease-2019-testing-basics from the FDA website makes all of this clear.

Since there is no current page in Wikipedia for "Positivity Rate" perhaps there should be one since it appears that a simple one line definition cannot explain adequately.

Wmccrack (talk) 15:52, 12 November 2020 (UTC)