Many novice users call and ask us about 'mfi' of their data. Since the acronym is ambiguous, we ask the scientist to specify if they are asking about **m**edian, **m**ean, or geometric **m**ean fluorescence intensity.

Mean and Geometric mean are easiest to understand - here are their formulae (from wikipedia):

Mean (aka arithmetic average) is defined as the sum of N things divided by N:

If your data is scaled in Log, you might want to use the log-friendly version of Mean, the Geometric Mean. This expression takes the Nth root of the product of N things:

Median is the number which divides the first half of your data from the second half, if sorted by some variable. Suppose you had 1 event with fluorescence of "262144" and 19 events with fluorescence of "1". The "mean" fluorescence would be (262144+19)/20 = 13108.

The Median fluorescence is 1 - if we sort the events by fluorescence and divide them in two parts, half of the events will have intensity no less than 1, the other half, no more than 1.

Depending on how you look at your data, Median usually gives the representation of a "typical" event. In the example above, no single event had fluorescence of "13108" which is what Mean would have us believe!

Also here is an interesting figure demonstrating the relationship of mode/median/mean in some types of distributions.

Courtesy of Jerrold H. Zar from Biostatistical Analysis, fourth edition, Simon & Schuester 1999

What does mode mean?

When do I use median fluorescence intensity?

thanks

Posted by: Anke | January 24, 2008 at 07:09 AM

Anke,

In statistics, mode is defined as the value with the most observations.

Median is good to use when you have non-standard distributions.

Posted by: Maciej Simm | January 24, 2008 at 12:21 PM

has anyone ever had a negative MFI value? some of my data is negative. is this possible? thanks.

Posted by: paulette | May 21, 2014 at 08:32 PM

X geo mean is the value of mean flourescent index???

how to calculate MFI?

Posted by: Aisha Arshad | October 26, 2016 at 01:58 PM

Does anyone have a suggestion for calculation of the percentage of events below the mode?

Posted by: Patrick | May 12, 2017 at 11:29 AM

Hi! is there a way to present the geometric mean

as a line on a histogram?

Posted by: Armen | August 30, 2017 at 03:37 PM

Hi, Does anyone use FlowJo for Bacteria for analyzing MFI?

Posted by: Wube | April 19, 2018 at 01:51 AM