What are the two major threats to internal validity in within-subjects experiments?

What should be on the medication label for medications in the monel cup on sterile field? 

What technique is used for delicate retractors? 

When should the surgical time-out performed? 

Observing a person’s behavior while having him or her complete a problem-solving task in the laboratory is an example of participant observation.

Who is primarily the person who will do the skin prep on the patient?  

What is the ability to predict the needs of the surgeon during case management called? 

One advantage of Likert-type rating scale questions is that they produce numerical scores that can be evaluated with standard statistical methods such as computing means.

Preventing an extraneous variable from becoming a confounding variable by holding it constant can result in a threat to external validity.

Nonexperimental studies always contain a threat to internal validity, which means that these studies cannot establish unambiguous cause-and-effect relationships.