Analysts spend thousands of hours trying to mathematically determine what will trigger the next rally and how long it will last. Technical analysis is especially prevalent in this effort, although less sophisticated indicators such as hemline fashions or the NFL division of the latest Super Bowl winner also provide fodder for such predictions. This in turn can sometimes lead to speculation that a rally is just around the corner, which can then become a self-fulfilling prophecy.
Rising investor confidence also indicates a rally, and it is perhaps more powerful than any economic indicator because when investors believe something is going to happen (a rally, for example), they tend to take action (purchasing shares in order to profit from expected price increases) that actually turn expectations into reality. Although it is an objective concept, investor sentiment shows through in mathematical measurements such as the put/call ratio, the advance/decline line, IPO activity, and the amount of outstanding margin debt.