Here's why investors shouldn't compare the coronavirus outbreak to SARS

It's now spread to more than two dozen countries, and on Tuesday the WHO chief said it's a "very grave threat" to the rest of the world, according to a report from Reuters.DataTrek Research co-founder Nicholas Colas also pointed to a very different geopolitical backdrop during the SARS epidemic, since it coincided with the runup to the war in Iraq and fears of an oil shortage."It is useless to compare how US/global equities fared under SARS in 2003 to the coronavirus today; the invasion of Iraq was the real catalyst for investor sentiment during this time," Colas said in a note to clients Tuesday.While the full impact of the virus will not, of course, be felt until it runs its course, a number of companies have already mentioned the impact on their revenue.On Tuesday, Under Armour said it expects the virus will cut sales by as much as $60 million during the first quarter, while Hasbro's senior vice president of investor relations, Deb Hancock, said on the company's fourth-quarter earnings call that "it's challenging to quantify the potential magnitude at this time."During Apple's first-quarter earnings call on Jan. 28, CEO Tim Cook said the company gave a wider than usual range for forward guidance given the "greater uncertainty" surrounding the ongoing impacts of the outbreak.Despite individual companies warning about weakness caused by the outbreak, the wider market has shown resilience.