One indication of the importance of replication is found in the 50 or more calls for replication research in the field of second language (L2) research alone (see references for 50 calls and commentaries in Appendix S1 in the Supporting Information online): from Santos (1989) through Polio and Gass 1997 to very recent proposals for specific replication studies, such as Vandergrift and Cross 2017 and even a book - length treatment (Porte, 2012).