Eight samples are tested on an ELISA plate…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Eight samples are tested on an ELISA plate. The readings are , , , , , , and for samples to . A sample is positive when its reading is above the cutoff of .
- How many samples are positive?
- What per cent of the samples are positive?
- Is sample positive?
Need a reminder? The key ideaShow
In allergy, IgE on mast cells makes the cells release histamine and serotonin. HIV is a retrovirus that destroys the helper T cells. A count below 200 helper T cells in each mm³ of blood is the sign of AIDS. In an ELISA plate a sample is positive when its reading is above the cutoff.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Eight readings and a cutoff of .
Plan. Compare each reading with the cutoff and count.
Step 1. The positive samples. The readings above are (sample ), (sample ), (sample ) and (sample ). That is samples.
Step 2. The per cent. .
Step 3. Sample . Its reading is equal to the cutoff, not above it. So it is not positive.
Answer: samples; ; no.
Check. The four others have readings of , , and , which are all at or below the cutoff.
Watch out. A single ELISA result is a screening test. Doctors confirm a positive result with further tests.
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