With thousands of donors for McCain and Obama, the authors wanted to analyze the types of people donating by examining the top 250 job titles for each candidate and trying to determine how much influence they have on the overall donations viewed in their previous visualization.
Since the donation information must be disclosed to the public, they turned to the Federal Election Commission to find a data set containing all donors, the amount they donated as well as other information the authors may try to explore next (i.e. occupation, zip code, employer).
The first image represents all donations made to Obama, and the second to McCain. The job titles (on the left side of the arc), start from the most common (Retired for both) on the left to the least common (of the top 250 titles) on the right. The right side of the arc is segmented into dollar brackets. The left bracket are amounts less than $100, the second is $100 to $500, the third is $500 to $1000 and the last (the largest) is over $1000. Also, the size of the right side ($ amount) segments are sized according to the total percentage of donation amount from the donors listed.
The most obvious result is that the most common donors for both candidates donated in the top-most $ amount bracket. However, for McCain, the top-most doners dominated his higher dollar brackets while the lower two are very mixed. In Obama's chart, we see a more dominant role of the less common doners in the $100 > $500 bracket. Also, Obama's lower (< $100) bracket is larger than McCain's.