He writes

the Dow is a crummily constructed index covering a small and curious sample of companies. If you really wanted to know how the stock prices of that curious sample of companies were moving, you’d really want to see some proper weighting going on. But how many of the people looking at the Dow know, or care, about this weighting? How many know, or care, about the identify of the companies in the index? Are we sure that the S&P is a more accurate measure of market movements? What sort of movements are we interested in anyway?

This can’t be said enough. Sometimes its worth, you know giving the data at least a cursory look. You see this in index construction all the time. Folks will moan to high heaven about how this index is fundamentally flawed.

But, then you take an index which analytically must be overstating the underlying concept you are interested in and one that must be understated. Put them together and you can’t see a difference. Does it stop the moaning? Unfortunately, not.

Some things matter, but most things don’t.