Do you have a positive result from the counter-test? It will probably be a mistake

The massive test Czech population is in full swing. Not everyone who tested positive actually met the coronavirus bag. The virus is probably still rare in our country, so in most cases it is probably a false alarm. N nstroj vm nzorn uke, for that it is so.

The test population of the test population can help answer an important question with epidemiologists: how many people have come into contact with the new coronavirus. So how is the prominence of the esk population. In addition to the volunteers, a statistically appropriate sample of the population is contacted to ensure that the results are representative.

During the two-day event study of collective immunity SARS-CoV-2-CZ-Preval m bt 27 thousand people will be tested by a rapid test, which looks for specific antibodies in the blood of those tested. This rapid test will respond within 20 minutes. If positive, the patient is advised to isolate himself in case an accident occurs. And for a while, the laboratory does not test it with a PCR test, which would reveal a possible ongoing infection, which lasts about two days.

If someone has a positive result (ie for antibodies and PCR test), it should be very small, but they can occur. In general, based on the results of the assumptions – and suppose the authors do – the vast majority of people will pass the first test negative.

But what about those who do well? How is it that the SARS-CoV-2 virus actually has in their blood? And what is the ance that this is a false alarm (so-called false positive)? We have created an interactive graph in which you can test how the birth of the infection in the population, the reliability of the test and the number of falench alarms are related.

Interactive graph
reliability of testing

The following is an interactive graph illustrated only.

  • It’s not both simulation and prediction
  • Nen to epidemiologick model
  • It does not contain reln data
  • Do not predict how many people become infected with coronavirus

The aim of the graph is to show the principle of test reliability and especially the verticality of the “falench” can be found on the reliability of the test used.


Reliability test – illustration

Poet testovanch: 1tisc member

Prevalence in the population: 1

Specific text: 95

Text sensitivity:95

more set
Nakaen Hello Total
Shot rod
Positive result
Negativn vsledek
Warning: this simulation or prediction of contagion. Slou vhradn
for illustration.

Each laboratory test has a certain reliability. The quality of the test is usually assessed according to two values:

  • Sensitivity indicates the probability that the infection will be correctly diagnosed with this test as the infection, ie how much of the total sweat the test will reveal.
  • Specificity on the contrary, it is likely that a test in people without disease will really show that they are healthy. Otherwise, how many true (true) negative results have resulted in all really healthy people.

The test used in the esk study had both values, ie specificity and sensitivity, 95 percent. In other words, 95 percent of people who have SARS-CoV-2 counteracts should first detect their presence. And the first result should be determined even by 95 percent of those who do not have counterparts.

In the interactive tool you can change these quantities and test in practice how their values ​​reflect on the falench test. And with realistic values, it turns out that most people who have a positive find is a false alarm (so-called false positive).

The reason is the low expected prevalence of the disease. Even the test, which is very accurate, will, in a small proportion of untrained people, report the disease. And if, according to nakaench in the population had, the result is a large amount of falench alarm. Paradoxically, even a very reliable test was found in most positive findings. Also, this phenomenon is not limited to the rapid test in the study – in a situation where the infection is rare, it is a general phenomenon. Of course, this does not mean that people with a positive result should not follow the recommendations of hygienists or avoid quarantine!

If such a result is surprising for vs, you are not alone. Even professionals (lkai) swim in these probable paradoxes. In 1995, researchers showed that only 8% of students could correctly estimate the frequency of a false alarm (PDF). The need for elephant probabilities is difficult and confusing. We hope that our interactive calculator can better understand this connection.