Yale Index Shows Declining Valuation Confidence [View article]
The chart would appear to make more sense if the S&P were graphed as some percent of over or undervalued rather than as an absolute value, then you would see a correlation between confidence and over or undervaluation. In other words, the SP going up or down doesn't tell you anything about whether or not it is over or undervalued.
Yale Index Shows Declining Valuation Confidence [View article]