You're correct. What saalweachter was describing are ways to minimize threats to reliability and validity.

- http://www.socialresearchmethods.net/kb/relandval.php

- http://www.mathcs.duq.edu/~packer/Courses/Psy624/Validity.ht...

- https://en.wikipedia.org/wiki/Internal_validity

- https://en.wikipedia.org/wiki/External_validity