1
$\begingroup$

I got a list of Influenza-specific antibody titers from a hemagglutination inhibition assay.

They look like this:

  • 40
  • 640
  • 160
  • <10

One site says: “The swine influenza HI scale is geometric: 20, 40, 80, 160, 320, 640 (successive values increase by a factor of 2). The geometric scale is logarithmic. It is best to express an average influenza HI titer as a geometric mean. A geometric mean is calculated by averaging the logarithms of the test values and then converting the mean to a real number. This prevents a few obviously high positive values from making the mean unrealistically large.”

What does that mean for my sample? How do I deal with <10 in this calculation? This is surely not rocket science, but honestly I don’t get it right now.

$\endgroup$
1
$\begingroup$

Typically "<10" is converted to a number that is below the limit of detection; often "9". After that simply following the instructions you have yields a GMT of 77.9. If you are using spreadsheet apps such as Excel or Google Sheets, they almost certainly offer "GEOMEAN" functions which will give the number directly.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.