A recent question here prompted me to ask the more fundamental question of whether the fees charged by professional advisors can be shown to be worth it.

Many consulting firms certainly claim their advice adds value. Here is the claim from Mckinsey:

Our mission is to help our clients make distinctive, lasting, and substantial improvements in their performance ...

Accenture's slogan is:

High performance: Delivered.

or variants thereof.

While there is a lot of cynicism about the value of consultants, the obvious retort is that clients would not keep buying advice if it didn't work. On the other hand the old joke goes:

A consultant is someone who borrows your watch to tell you the time.

(Some consultants, not me, obviously, might respond that clients are people with watches who can't tell the time).

But, aside from anecdote, is there any objective evidence that consulting advice is worth paying for?

Full disclosure: I work for a consulting firm.