Add note about definitions

doc/development/open-questions/index.mdwn

@@ -127,3 +127,9 @@ Discussion of metacognitive strategies that could have computer aides.
     * <http://www.pz.harvard.edu/thinking-routines>
     * <https://www.sadlier.com/school/ela-blog/think-puzzle-explore-visible-thinking-routine-a-professional-development-series>
     * <https://thinkingpathwayz.weebly.com/thinkingroutines.html>
+- Be clear about definitions
+    * e.g., economic variables such as productivity can vary in definition
+      based on if you are working in micro- or macro- contexts.
+    * e.g., GDP is not always computed directly from national income data, but in
+      some cases may be partially imputed.
+    * e.g., explain how life expectancy is computed.