Why are reliability and validity such important principles in psychological measurement?

The FOUR essay questions are:
1) “The scientific method provides the best way to answer questions, explain causal relationships in nature, and test the effectiveness of treatments.”
–  Do you agree with this statement?
–  Take a position on this question.
o In answering this question, make sure to contrast the scientific approach with one of the non-scientific methods of knowledge acquisition that were discussed in lectures, perhaps in the context of a real or hypothetical research question.
2) What is the best design for an intervention study, and why?
–  Describe a hypothetical intervention study and outline how you would design such a study.
–  Make sure that you describe all of the essential features of the design that you choose.

3) Why are reliability and validity such important principles in psychological measurement?
–  Make sure you clearly define both terms in your answer.
–  In answering this question, consider a scenario where an important decision is made about a person on the basis of a psychological test.
o Why would reliability and validity be important in this situation, and what might be the consequence of using a test with poor psychometric properties?

4) “When—if ever—is deception acceptable in psychological research?”
–  Describe the ethical principles that support your position.
–  Give an example of the use of deception in psychological research (either real or fabricated)
to illustrate your answer and support your view.”