diff --git a/lectures/_static/quant-econ.bib b/lectures/_static/quant-econ.bib
index 1c32e7f..fa2b46a 100644
--- a/lectures/_static/quant-econ.bib
+++ b/lectures/_static/quant-econ.bib
@@ -2369,6 +2369,25 @@ @article{Jacobson_73
     pages = "124-131"
 }
 
+@article{wallis1980statistical,
+    author = "Wallis, W Allen",
+    title = "The statistical research group, 1942--1945",
+    journal = "Journal of the American Statistical Association",
+    volume = "75",
+    number = "370",
+    pages = "320--330",
+    year = "1980",
+    publisher = "Taylor \\& Francis"
+}
+
+@book{Burns_2023,
+    author = "Burns, Jennifer",
+    title = "Milton Friedman: The Last Conservative by Jennifer Burns",
+    year = "2023",
+    publisher = "Farrar, Straus, and Giroux",
+    address = "New York"
+}
+
 @article{Orcutt_Winokur_69,
     author = "Orcutt, Guy H. and Winokur, Herbert S.",
     issn = "00129682, 14680262",
diff --git a/lectures/wald_friedman.md b/lectures/wald_friedman.md
index 31517b4..f5c4f85 100644
--- a/lectures/wald_friedman.md
+++ b/lectures/wald_friedman.md
@@ -83,6 +83,11 @@ Milton Friedman described a problem presented to him and Allen Wallis
 during World War II, when they worked at the US Government's
 Statistical Research Group at Columbia University.
 
+```{note}
+See pages 25 and 26  of Allen Wallis's 1980 article {cite}`wallis1980statistical`  about the Statistical Research Group at Columbia University during World War II for his account of the episode and  for important contributions  that Harold Hotelling made to formulating the problem.   Also see  chapter 5 of Jennifer Burns book about
+Milton Friedman {cite}`Burns_2023`.
+```
+
 Let's listen to Milton Friedman tell us what happened
 
 > In order to understand the story, it is necessary to have an idea of a