Can anyone please help me to understand the values in Von Frey 50% threshold calculation. I have difficulty in calculating the δ value. Is it the difference between two filaments applied? I am using the Ugo Basil von Frey filaments and Up-down method.
Thanks in advance,
Sigma is the mean difference in your set of filaments, but in log units. However, I’ll also say that I don’t know of anyone who calculates their 50% thresholds totally by hand. I’d check out this 2020 paper by Christensen et al. for more info on how thresholds are estimated, some pitfalls of the common method, and a way to get around them using an online calculator. https://onlinelibrary.wiley.com/doi/10.1002/ejp.1528
There are also several other ways of estimating PWT that, while imperfect, are more intuitive and a bit faster.
People argue about how this should be done most perfectly, but at the end of the day, the VFT is already imperfect enough, and exact quantification method probably won’t do much to change your conclusions.