Tenets of investment, upended

Faith in correlations has been sorely tested as markets tear up one long-held maxim after another

You don’t need a PhD in theoretical physics to know that market correlations have been behaving badly of late. But to understand why, a doctorate might not help anyway.

Peter Shepard, one of the brains behind MSCI’s widely used Barra risk models, studied string theory and the quantum theory of gravity at the University of California, Berkeley, where he earned his degree.

But even he is scratching his head over the lengthening list of correlations falling apart simultaneously across global