This is one of the most important indicators for measuring participation. The 200-day moving average is a long-term smoothing of price movement, and a stock's price in relation to this moving average is a good indication of its long-term trend. For example, when the price index moves below the 200-day moving average, we can assume the long-term trend is down until the price index moves back above the 200-day moving average.

There are no automatic assumptions that can be made about this index. For example, just because 80% of stocks are above their 200-day moving average, there is no guarantee that a downside reversal can't happen. In fact, once the index has moved to an extreme end of its range, it's a good idea to be alert for a change in direction, because the market improves until it is as good as it can get, then it starts to deteriorate. Conversely, as soon as things are as bad as they can get, they start improving.

The most important aspect of this indicator is the trend. When the market is trending upward this index should be also be trending up. A trend divergence indicates that fewer and fewer stocks are in sync with the price trend and that a price reversal is likely.