Here’s what’s led stocks from bull market to bear market and back again

On March 24, 2000, at the peak of the dot-com bubble, the technology sector made up a staggering 34.5% of the S&P 500 by market cap. At the ensuing bottom, on Oct. 9, 2002, it had deflated by nearly two-thirds, accounting for less than 13% of the overall market. Here’s a look at the changing composition of the market through ups and downs.