COVID Chronicles: When Data Don’t Match the Message

A curious thing happens if you Google Los Angeles County coronavirus – you see a lot of positive messaging.

My favorite thus far is “No coronavirus surge post-Labor Day in LA County, officials say” (link below). Quoted in the article is LA County Health Director Dr. Barbara Ferrer who says, “That’s in part because people took actions to make sure we didn’t see that surge.”

Other headlines include:”No Post-Labor Day Spike In COVID Cases Pushes LA County Closer To Reopening””LA County COVID-19 Hospitalizations Continue Decline, Approach Early Pandemic Levels””Los Angeles County Coronavirus Update: L.A. Records Only 1 Death Related To COVID-19 On Monday; No Labor Day Surge Emerges; Lowest Total Since March”

As a graduate student in Epidemiology, I took a seminar in outbreak investigation. A fundamental exercise was simply looking at an epidemic curve and being asked “what do you see?”

Let’s do the same exercise with Los Angeles’ coronavirus epidemic curve (Figure 1 below). What do we see? We have a graph showing essentially a steady uptrend to a July 17th peak with a rapid acceleration beginning June 19th. The curve the drops quite steadily until 9/11. But the last two weeks have shown increases – from 7.77 new daily cases per 100,000 population the week of 9/11 to 8.71 and 9.04. This is a 16.3% increase.

On July 3rd the Los Angeles County case rate stood at 26.89. On July 17th, that rate hit its maximum of 29.47 – a 9.6% increase. By my math, a 16.3% increase is greater than a 9.6% increase. So, if we are calling the July 4th increase a ‘surge’, then the percentage increase since Labor Day is even more of a dramatic surge.

The process of looking further into data is best summed up in Hans Rosling’s book Factfulness (which I cannot recommend highly enough). In it, he says ““If you are offered one number, always ask for at least one more. Something to compare it with.”

In this case – if you are told that there is no ‘surge’, it is worthwhile asking Dr. Ferrer how she defines a “surge” numerically. Because it sure seems like we are having one, when you compare July 4th to Labor Day.


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