Minor typo

efect -> effect

ipynb/Economics.ipynb

@@ -1122,7 +1122,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "It is still surprising that we still have no efect from restricting trade."
+    "It is still surprising that we still have no effect from restricting trade."
    ]
   },
   {