The index represents all sectors of the U.S. economy, and includes both the Growth and Value investing styles. But a truly diversified investor might consider elements with a low correlation to the index, which consists mostly of stocks with fairly large market capitalizations. The Russell 2000 Index is usually considered a surrogate for Small Cap Growth issues. And, according to Bloomberg, the two indexes have performed differently. This was a very interesting time for the indexes, since it includes a bull market run-up in overall stock valuations, followed by a significant decline.
Indexes move both ways, of course.
That, of course, is the whole point of having exposure to both. Stock prices tend to be driven by earnings growth. The smaller the base, the easier it can be to post an impressive gain. Often smaller companies have a single, limited product. The market for their particular widgets may behave differently than the broad economy.