The rule says that the percentage of the vote a sitting president gets in polls is a better indicator of the state of the race than the margin.

ECONOMIST: After the debates

Margin debt, a seldom-referenced indicator of confidence and speculation has contracted on a yearly percentage change as much as in the bear markets of '74, '82, '87 and '01.

FORBES: Manic Depression To Normalization

In fact, with GDP growth generally a lagging indicator anyhow, it is often more rewarding to pay attention to policies at the margin that encourage economic growth when trying to predict outperforming global markets, says Vlad Signorelli, global research director at boutique investment research firm Brettonwoods Research LLC in New Jersey.

FORBES: 19 Reasons Why Emerging Markets Belong In Your Portfolio