“The stock market is a voting machine rather than a weighing machine. It responds to factual data not directly, but only as they affect the decisions of buyers and sellers.”- Graham and Dodd, Security Analysis

Earnings drive stock prices – so says investing lore. As earnings rise or fall, stock prices move higher or lower by a commensurate amount.

Is this actually how it works?

At first blush, it certainly seems so. In looking at a simple chart, earnings and stock prices appear to move closely together.

Data Source: YCharts. Date Range: 1988 – 2017.

But appearances can be deceiving. While earnings and stock prices tend to move together over long periods of time, in the short run there can be wide divergences.

In any given year, predicting the change in the S&P 500 based on the change in earnings is a difficult game to play. There have been years in which earnings have declined but stocks finished higher (1991 and 2007) and years in which earnings have increased but stocks finished lower (1994, 2000, 2002 and 2011).

In most years (79% of the time since 1989), earnings and stock prices move in the same direction, but the magnitude is far from equivalent. For example, in 1998 earnings rose 0.6% while stock prices advanced 26.7%. In 2001, earnings declined 30.8% while stock prices declined only 13.0%.

Data Source: YCharts. Note: S&P 500 returns in this table are based on index price levels, not total return including dividends. EPS = Earnings Per Share. 

What is the source of these discrepancies?

Changes in investor sentiment, what Graham and Dodd called the “voting machine.” This change in sentiment leads to expansion or contraction in multiples (ex: P/E ratio) that oftentimes supersedes changes in earnings.

1991 is perhaps the best example of this phenomenon when earnings fell 14.8% while stock prices rose 26.3%. The result: a multiple expansion of over 48%, moving the P/E ratio on the S&P 500 from 14.6 to 21.6.

Data Source: YCharts. Note: S&P 500 returns in this table are based on index price levels, not total return including dividends. P/E = Price to Earnings Ratio.

When changes in prices exceed changes in earnings, multiples expand. When changes in earnings exceed changes in prices, multiples contract.

Over the past six years (2012 – 2017), multiples have expanded every year as gains in the S&P 500 have outpaced gains in earnings.

Will multiples expand again in 2018?

As we have seen, the answer to that question will depend not only on changes in earnings but also changes in sentiment.

According to S&P Dow Jones, operating earnings are expected to increase 24.8% in 2018, (moving from $125 to $156), the largest increase since 2010.

If these expectations are met and the S&P 500 finishes the year higher by 24.8%, the P/E multiple will remain unchanged at 21.4.

Data Source: YCharts. Note: These are hypothetical assumptions for year-end 2018.

While it’s possible that happens, it should by no means be expected. In 62% of years since 1989, there has been more than a 10% change in the P/E multiple.

Data Source: YCharts.

Why would multiples expand or contract this year? Any number of reasons: changes in future earnings expectations, economic conditions, central bank policy, interest rates, inflation, geopolitics, etc.

Basically, anything that influences investor sentiment can have an impact on the multiple investors choose to pay today for a given level of earnings. Needless to say, predicting investor sentiment is a difficult game, which in turn makes predicting future stock prices exceedingly difficult. Further complicating matters is the fact that predicting future earnings is not any easier.

The good news is that you don’t have to predict such things to reap the benefits of being invested in a diversified portfolio over time. In fact, predicting often does more harm than good as it can lead to taking unwarranted and deleterious actions in your portfolio. The next time someone asks you where you think stocks, earnings and multiples are going, don’t be afraid to say “I don’t know.”