Last week I've shared with you my Institutional Investor article on some important but quite boring topics that include the Fed Model, the price-to-earnings ratio, and profit margins. I imagine for most civilians (people who don't do investing for a living) reading about these topics is as exciting as watching a live debate between two paleontologists about how the size of tyrannosaurus' front teeth relates to the length of spinosaurus' tail. (I have no idea what I just wrote.)
I will have you know, however, that the Fed Model is extremely important, because I vividly remember how low interest rates and the Fed Model were used as propaganda tool in the late '90s to justify the stock market's 'this time is different' sky-high valuation. Low interest rates have been pushing investors into riskier assets and have thus resulted in higher valuations, but just as you would expect a finite boost of energy from 5-Hour Energy drink, low interest rates will not bring permanently higher valuations in stocks.
I see an army of experts on business TV - and non-experts in day-to-day dealings - justify holding otherwise overvalued stocks by comparing their yields of 2% or 3% to the yields of bonds. Stocks and bonds are competing assets, so a low yield in bonds in the short term (a key distinction) will drive higher P/Es (lower earnings yields) in stocks. But today, rather than a race to the top we have a race to the bottom. As bonds yields rise (or not - if they don't it means we're in deflation, which is even worse) stock valuations will return to their rightful place - lower. Of course there is a caveat: they may go a lot higher before they do that. But that's investing for you.
I have written the topic of profit margins half to death; I even penned a scribble for Barron's, discussing them back in 2008. All you have to do is look at the historical charts (see this chart) - profits always mean-revert. Mean reversion of profits is so banal it should be taught in finance classes just as Newton's law of gravitation is taught in physics. Earnings have never grown at a faster rate than GDP (sales of the economy) for a substantial period of time. This time is not different. I'd buy an argument that the long-term mean of profit margins may have shifted upwards over the last two decades as we have become more of a service and less of a manufacturing economy. So instead of being at 8% - or maybe it should be closer to 9% - we are in the mid-teens.