What factors influence the performance of these indexes?What type of indexes are the S&P 500, DJIA, and NASDAQ Composite?

In this part of the project, we will investigate three stock market indexes: S&P 500, Dow Jones Industrial Average , and the NASDAQ Composite.
From the Yahoo! Finance home page:
• Click on “S&P 500” on the front page. The original graph shows the index for the current business day.
• Change the view to the full screen, then change the view to two years .
• Using the +Comparison button above the graph, add DOW and NASDAQ to the
graph to show the percentage change for each day relative to the first day and the level of each index.
Write a report analyzing the results you received. At a minimum, respond to all of the following:
• What type of indexes are the S&P 500, DJIA, and NASDAQ Composite?
• What factors influence the performance of these indexes?
• Is there a difference between the performances of S&P 500, DJIA, and NASDAQ
Composite over these two years? If so, explain the factors that contribute to those
differences.