You asked
The Office of National Statistics derives estimates of Covid-19 prevalence in the community population of England. I understand that the ONS tests a random sample of the population using a PCR test and the number of tests reported as positive includes those who are, and are not, symptomatic. On that basis, I have the following questions:
Since March 2020, until the present:
What cycle threshold value or values have been used by the ONS in its random testing?
What has been the a) number and b) proportion of tests done for each cycle threshold value used?
Where the cycle threshold value used has been changed, please give the dates on which the value was changed and the reasons for change.
We said
Thank you for your request.
The PCR tests used for our survey are accredited tests and part of the national testing programme. The swabs are processed by the Lighthouse Laboratories in Glasgow, and the UK Biobank centre are responsible for setting the Ct threshold of positive tests. More information about our swab procedure can be found in our methodology article or our study protocol.
In the technical dataset accompanying our latest bulletin, you can find the genetic lineages and Ct values of a sample of the positive tests returned by the participants in our study on tab 1a.
In the same dataset, on tab 2f, you can find the total number of tests performed daily since the survey began.