Extraneous & dependent variables and levels of evidence discussion essay

Answers to questions expected to be 150 words. Provide two or more references for each question using in-text citations and source referencing in APA 6th ed. formatting (see announcement on APA 6th ed. formatting). No title page or running header needed.

DQ #1
Extraneous variables may have an influence on the dependent variable. In what ways do researchers attempt to control extraneous variables? Support your answer with current literature.