Sam Walton, the founder of Walmart, the world's biggest supermarket group, used to say he liked seeing dead animals on the road.
He thought roadkill was a good indicator of economic activity - the more dead animals, the more his trucks were travelling.
There are other indices of economic activity.
An American economist came up with the Garbage Index. More rubbish being put out indicates the economy is growing a bit faster.
Lipstick manufacturers tend to do well in recessions. Don't laugh: the research was published in 2012 in the ultra-reputable Scientific American. Maybe tastes have changed. Maybe not.
The author explained: "While periods of abundance favour strategies associated with postponing reproduction in favor of one's own development (e.g. by pursuing an education), periods of scarcity favor more immediate reproduction."
She elaborated on why sales of "lipstick and designer jeans, high-heeled boots and perfume" rise in difficult economic times: "Our findings consistently supported the lipstick effect, as college-age women, when primed with news of economic instability, reported an increased desire to buy attractiveness-enhancing goods, along with a decreased desire to purchase goods that do not enhance one's physical appearance."
And now, after the roadkill, rubbish and lipstick indices, we have the toilet-paper index.
It is not, though, an economic indicator but more a signifier of fear.
In March, the shelves were cleared of toilet paper as people panic-bought for fear of the oncoming virus crisis.
And now, the fear is back. Woolworths and Coles have started limiting sales again, foolish though Prime Minister Scott Morrison thought it.
"Stop it, it's ridiculous," he said. And he is right. No doubt about it.
But empty shelves warp minds. We panic-buy because others have panic-bought.
"In times of stress, emotions are heightened, and consumers feel more pressured to buy on the spot when they see something that is high in demand becoming scarcer," according to Nitika Garg, an associate professor of marketing at the University of New South Wales.
The researcher into the relationship between emotion and shopping cautioned against more madness in coming weeks.
"Many people in China are stocking up on toilet paper to make their own masks as a result of the mask shortage," she said.
"This is not a solution and people in Australia should not be encouraged to stock up on toilet paper to make homemade masks."
I won't - but then again, I've still got 12 rolls I bought on eBay from China back in March.