Internal vs. External Validity

When looking at different research studies, you will often find that when internal validity is high, external validity is low, and vice versa.  Further explore the interaction between internal and external validity.
Tasks:
Part 1:
Based on research,  2 pages:
•    What is internal and external validity? When conducting research, why is there often a trade-off between internal and external validity?
•    Is there a benefit in achieving a high level of one type of validity (internal versus external) over the other? Is there a way to design a study or series of studies to have high internal as well as high external validity? What would be the benefit?
Part 2:  (1) pg.
 Locate a research study related to the human services field. Share your purpose of research.
•    Evaluate the level of internal and external validity achieved in the study.
•    Discuss how the interpretation of the data is affected by the level of validity (both strengths and weaknesses).

One Reference: Reading and Understanding Research
3rd ed.
Lawrence F. Locke
The University of Massachusetts at Amherst
Stephen J. Silverman
Teachers College, Columbia University