The big oil and gas firms account for more than half of the Russian Trading System stock index, which is the reason why the Russian trade is so highly correlated to oil futures.
Its report grades cities using, in part, the EPA's color-coded Air Quality Index, as well as its own weighting system that ranks the severity of pollution on a daily basis.
Heart-rate variability, says Dr Stein, is a good indexof the degree of control an individual has over his autonomic nervous system (which controls many of the internal organs).