S&P changes weightings

Standard & Poor's will change the weighting of many of its shares

Standard & Poor's on Friday will make one of the most significant changes to the prestigious S&P 500 index of stocks since its inception 80 years ago.

The S&P 500, a widely followed barometer of how the stock market is doing, will, after the market's close that day, change the weightings of many of its shares, effectively reducing the influence that some carry and increasing the clout of others.
S&P will make the same changes to its SmallCap 600 and MidCap 400 indexes.

All three indexes are "market-weighted," meaning their biggest stocks, by market capitalization, move the indexes more than those with lower market caps.

Under the new initiative, called the "full float adjustment," S&P aims to increase liquidity, or ease of trading, by reducing the influence of stocks with a lot of shares that are not publicly traded for reasons of their being held by a founding family or a government entity.