1) Choose one of the four following approaches:

• Instrumental
• Fixed Effects
• Diff-in-Diff
• Panel Data

2)Why is this approach used? What problem with data and/or the ordinary least squares ("OLS", i.e. standard multivariate regression approach) does this approach attempt to correct?

3) Explain briefly how this approach is implemented.

Please include references for all answers :)

Thank you much!