An indexs price can be affected by a range of factors, including: Economic news investor sentiment, central bank announcements, payroll reports or other economic events can affect underlying volatility, which can cause an indexs price to move Company financial results individual company profits and losses will cause share prices to increase or decrease, which can affect an indexs price Company announcements changes to company leadership or possible mergers will likely affect share prices, which can have either a positive or negative effect on an indexs price Changes to an indexs composition weighted indices can see their prices shift when companies are added or removed, as traders adjust their positions to account for the new composition Commodity prices various commodities will affect different indices prices. For example, 15% of the shares listed on the FTSE 100 are commodity stocks, which means any fluctuations in the commodity market could affect the indexs price