Hello!

I've not used the Dixon method for von Frey before, and the maximum likelihood estimate certainly seems to be a complex thing but perhaps this might shed some light?

http://statgen.iop.kcl.ac.uk/bgim/mle/sslike_3.html

Otherwise, have you considered using other methods for von Frey? The DSFN have produced this paper detailing their methods for QST which cuold be of use:

http://www.ncbi.nlm.nih.gov/pubmed/16291301

von Frey is commonly used in pre-clinical studies so might be worth having a look at some of those for their methods. It's been a while since I have done it myself, but I used an up-down method, taking an average of the threshold value.

Also, this might give a few more pointers:

https://www.researchgate.net/post/Does_anybody_now_what_is_the_best_method_to_measure_mechanic_allodynia_with_von_Frey_filaments

Thank you so much Rosie!:)

The maximum likelihood estimate is quite complex and you don't really need to know how to compute it to calculate the EI50. Rather, you just need to have the tabulated k values and based on the pattern of responses (positive vs negative response). I don't know whether you have looked at Dixon's original paper, but the tabulated k values are there. I've attached the original Dixon paper and another paper of his where he explains the staircase method used for the up -down von Frey determination. Alternatively, in our lab we have developed a macro for calculating EI50. We use this macro for von Frey in mice, but it should work for QST if you change the values appropriately. If you are interested in the Macro then I can send it to your private email. Just send me a message.

Thank you Loren!