diff --git a/03-documentation/terms_of_reference-key_terms.md b/03-documentation/terms_of_reference-key_terms.md
index 2cdd956..03a5474 100644
--- a/03-documentation/terms_of_reference-key_terms.md
+++ b/03-documentation/terms_of_reference-key_terms.md
@@ -252,6 +252,8 @@ External Validity:
   sample, the ecological validity of the study conditions, and the relevance of the
   findings to real-world settings.
 
+good link: https://learning.edanz.com/validity-systematic-review/
+
 In summary, internal validity focuses on the accuracy and reliability of the study's
  findings within the specific context of the research, while external validity
  focuses on the generalizability and applicability of the findings to broader