SIPRI counts the deliveries of large conventional weapons, each of which is assigned a value according to cost, strategic importance and other criteria.

And shares that look cheap on conventional measures (asset value, dividend yield, price-earnings ratio) also tend to deliver above-average returns, but belong to firms that are likelier to go bust.

Though ETPs have been growing rapidly (see chart 2), their total value is less than $200 billion, less than one-seventh of that of conventional ETFs.