Why are random assignment and experimental control two essential ...

[michelleunicorn]

Why are random assignment and experimental control two essential ingredients of an experiment?
 
  What will be an ideal response?

Question 2

Dr. Malic has conducted a number of experiments to assess whether playing violent videogames makes people become more aggressive. He assigns men to play very violent games for an hour a week, and women to play very violent games for three hours a week.
 
  After a month, he assesses how aggressively they behave in a frustrating situation. He has replicated this study using the same sample of Buddhist monks and nuns twelve times. Identify the major threat to internal validity and to external validity.
 
  What will be an ideal response?

[carojassy25]

Answer to Question 1

Answer: Random assignment is the great equalizer, and ensures that groups of participants are comparable to one another before the delivery of the independent variable. Control over extraneous variables ensures that any differences on the dependent variable are due to the manipulation of the independent variable only.

Answer to Question 2

Answer: The threat to internal validity is that Dr. Malic has not used random assignment, thus he cannot be sure that he has isolated the independent variable: the amount of time playing violent video games. The threat to the external validity is that Dr. Malic used the same sample in his replications. Not only that, but his sample of clergy may not generalize to other people, especially when it comes to the behavior of aggression.