diff --git a/CALCULATE SPOTS DIFF.R b/CALCULATE SPOTS DIFF.R
index a4785be..645fdf1 100644
--- a/CALCULATE SPOTS DIFF.R	
+++ b/CALCULATE SPOTS DIFF.R	
@@ -1,3 +1,14 @@
+## This functions are adapted from Zoe Moodie version.
+## https://rundfr.fredhutch.org/
+## https://www.fredhutch.org/content/dam/www/research/divisions/vaccine-infectious-disease-division/staff-scientists/moodie/elsdfreq.R
+############
+## REFERENCE:
+## Cancer Immunol Immunother. 2010 Oct; 59(10): 1489.1501.
+## doi: 10.1007/s00262-010-0875-4
+## PMCID: PMC2909425
+## Response definition criteria for ELISPOT assays revisited
+## Z. Moodie, L. Price, C. Gouttefangeas, A. Mander, S. Janetzki, M. Loewer, M. J. P. Welters, C. Ottensmeier, S. H. van der Burg, and Cedrik M. Britten
+
 impose.mono <- function(x, dir){
   # Function to impose monotonicity on elements of the vector, x
   # dir="incr" gives increasing monotonicity