diff --git a/transform.Rmd b/transform.Rmd
index ae032c5..909da37 100644
--- a/transform.Rmd
+++ b/transform.Rmd
@@ -389,7 +389,7 @@ There are many functions for creating new variables that you can use with `mutat
     feature we'll come back to in modelling.
     
     All else being equal, I recommend using `log2()` because it's easy to
-    interpret: an difference of 1 on the log scale corresponds to doubling on
+    interpret: a difference of 1 on the log scale corresponds to doubling on
     the original scale and a difference of -1 corresponds to halving.
 
 *   Offsets: `lead()` and `lag()` allow you to refer to leading or lagging