Interesting. I suppose another possibility is that both tests were false positives. Unlikely assuming that false positives are independent—but is that a reasonable assumption here? It seems possible they’d be correlated—e.g. if the tests were picking up some other infection.
Does anyone have a good understanding of this (in general, needn’t be SARS-cov-2 specific)?
Under what circumstances is it (un)reasonable to assume that false positives are independent?
Sensitivity and specificity of the test. an image here
sensitivity = number of true positives / number of true positives + number of false negatives (true positives that test negative)
specificity = number of true negatives / number of true negatives + number of false positives (cross-reactions, other infections giving positive result)
Some info. I found here about covid19 PCR test. (It might not be the test that was was used but as far as I’m aware all current covid virus testing is via PCR so the tests should be of a very high specificity − 100%?!)
Contamination of swabs is a possibility for positive results in a negative patient. (e.g. test personal is positive and contaminates sample, contamination in lab.)
Poor technique on sampling, ‘bad luck’ just missing the virus on sampling, using the wrong type of swab, poor handing of sample will give a negative result for a positive case.
Interesting. I suppose another possibility is that both tests were false positives. Unlikely assuming that false positives are independent—but is that a reasonable assumption here? It seems possible they’d be correlated—e.g. if the tests were picking up some other infection.
Does anyone have a good understanding of this (in general, needn’t be SARS-cov-2 specific)?
Under what circumstances is it (un)reasonable to assume that false positives are independent?
Test reliability:
Sensitivity and specificity of the test. an image here
sensitivity = number of true positives / number of true positives + number of false negatives (true positives that test negative)
specificity = number of true negatives / number of true negatives + number of false positives (cross-reactions, other infections giving positive result)
Some info. I found here about covid19 PCR test. (It might not be the test that was was used but as far as I’m aware all current covid virus testing is via PCR so the tests should be of a very high specificity − 100%?!)
A bio-optical laser sensor for COVID testing is under development.
Technique/testing protocol.
Contamination of swabs is a possibility for positive results in a negative patient. (e.g. test personal is positive and contaminates sample, contamination in lab.)
Poor technique on sampling, ‘bad luck’ just missing the virus on sampling, using the wrong type of swab, poor handing of sample will give a negative result for a positive case.