ECO Paper - Concepts of Internal and External Validity

Suppose that you have just read a review of the literature of the effect of beauty on earnings. You were initially surprised to find a mild effect of beauty even on teaching evaluations at colleges. Intrigued by this effect, you consider explanations as to why more attractive individuals receive higher salaries. One of the possibilities you consider is that beauty may be a marker of performance/productivity. As a result, you set out to test whether or not more attractive individuals receive higher grades (cumulative GPA) at college. You happen to have access to individuals at two
highly selective liberal arts colleges nearby. One of these specializes in Economics and Government and incoming students have an average SAT of 2,100; the other is known for its engineering program and has an incoming SAT average of 2,200. Conducting a survey, where you offer students a small incentive to answer a few questions regarding their academic performance, and taking a picture of these individuals, you establish that there is no relationship between grades and beauty.

Write a short essay using some of the concepts of internal and external validity to determine if these results are likely to apply to universities in general.