Life is messy. Numbers are neat.
Or so I’ve liked to think. Math has been a comfort zone in times of confusion, a way to pick out signals in the noise, see patterns in chaos. At the least, it could provide a sense of boundaries, scaffolding, a handhold. With a little help from math, we can begin to grasp even concepts we’ll never really grok.
But now my friends the numbers seem to have deserted me—an insidious side effect of Covid-19. The blinding rain of data the virus unleashed can drown out more than it reveals. Downpours are opaque—a good reason not to drive in them or try to navigate through a crisis.
The worst offenders are the damned denominators—often unknown, unspoken, misused, dubious, deceptive, dopey, even demonic.
To a person of my vintage, denominators are personal. If I’m 73 years old today, what is my denominator? If it’s 74, it’s time to start saying goodbyes, putting my affairs in order, as they say. Anyone facing death is coming to terms with their life’s denominator, something a pandemic has a way of putting in perspective.
I hadn’t been thinking much about denominators until I got an email from Kathleen Hall Jamieson, the director of UPenn’s Annenberg Public Policy Center, where I’m currently a scholar-in-residence. “The number diagnosed is a bad denominator,” she wrote to her staff, way back on March 20, just as testing was ramping up. Scientists and journalists alike were basing fatality rates on “cases,” a number nobody really knows. Recovery rates were just as cloudy. “Recovered” implies a person was infected. But no one knows how many people who “recovered” from flu back in January and February (also) had the virus. They were almost certainly not counted as cases.
Often, denominators are simply disappeared. “US surpasses Italy in total deaths,” The New York Times (and others) all but screamed, conjuring images of corpses in the street. But the US was bound to have more fatalities; it has a lot more people. If you look at deaths per capita (denominator, please!), then the fatality rate in the US looks less bleak.
I have the same sort of “duh” response to continual reminders that for us elderly and people with pre-exiting conditions, the fatality rate is much higher. Higher than what, you might (you should) ask? What’s the denominator? Most old folks have pre-existing conditions, and age itself is, sooner or later, a cause of death. In a normal, non-Covid year, most people who die are over 80. The major causes of death are heart disease, cancer, stroke, injury, suicide. How do these diseases and conditions (pre-existing or not) interplay or overlap?
Among younger people, suicide and “unintentional accidents” (including homicide) are right up there with cancer and upper respiratory disease—both affected by air pollution, which we’re told is decreasing, thanks to people staying at home. At the same time, domestic violence is increasing, along with divorce (no surprise there). What effect does isolation have on mental health? On stress? Yes, people are standing in line to buy bleach and toilet paper, but they’re also buying guns.
Does it make any sense to try to compare such disparate types of risks when so little is known? Probably not a lot. Still, when scientists (and reporters) tell us more people will die if we do this or that, shouldn’t we know: more than what?
To compare anything at all, we need, at the least, some kind of base rate (a denominator): 1.2 percent of 382 million (US population) is a whole lot more than 1.2 percent of 60 million (Italy). If I tell you half of the homes on my street have swimming pools, you could conclude I live in a fancy neighborhood. Or you could ask: How many houses