Summarize the methodology and findings of Bertrand and Mullainathen

Summarize the methodology and findings of Bertrand and Mullainathen.  In your summary, be sure to clearly explain why a simple comparison of the outcomes of black and white people does not provide a good measure of discrimination. For example, if we want to know whether black people are discriminated against in terms of wages, why would comparing average wages of black and white people be insufficient?  Make sure that your explanation of Bertrand and Mullainathan's article explains how their study isolates discrimination from other factors.

Here is the link to the article: 

https://www.nber.org/system/files/working_papers/w9873/w9873.pdf