On a practical level, why wouldn't a researcher be likely to ...

[darbym82]

On a practical level, why wouldn't a researcher be likely to create an experiment with a 2x3x4x5 design?
 
  What will be an ideal response?

Question 2

What types of research can be exempt from Institutional Review Board (IRB) consideration, according to U.S. federal law?
 
  What will be an ideal response?

[Chocorrol77]

Answer to Question 1

An experiment with this design would include 120 conditions. That would mean that, with a between groups design, you would need 120 people to provide a single person in each condition, and you would never want a single person. If you wanted 10 people, which is still small, it would involve 1,200 people. If you used a repeated measures design, each person could in the extreme, be involved with 120 conditions, which wouldn't be practical.
In addition, it could be very difficult to interpret the interactions, especially if there were higher order interactions (e.g., three- or four-way interactions).

Answer to Question 2

Research conducted in established or commonly accepted educational settings, involving normal educational practices can be exempt from approval, such as the effects of different instructional strategies.
Research involving the use of educational tests, survey procedures, interview procedures or observation of public behavior. (Surveys and interviews on sensitive or controversial topics may require IRB approval, though.)
In addition, research involving public officials or political candidates can be exempt from IRB approval.
Research involving the collection or study of existing, publicly available data, documents, records, pathological specimens, or diagnostic specimens is exempt if the personal identity of those providing the data is protected.

[darbym82]

Excellent

[vickyvicksss]

Gracias!