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A Guide To Better Understanding New York City's COVID-19 Data

By

Elizabeth Kim

Published Oct 2, 2020

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New Yorkers riding subway with masks.

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By

Elizabeth Kim

Published Oct 2, 2020

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Before any vaccine becomes available, and even when it does, the best way for public health experts to arm themselves against coronavirus is by collecting and analyzing as much data as they can. But during the early days of the crisis, a lack of testing—the key data stream in public health—proved to be a crippling blindfold. New York City health officials struggled to figure out who in the city had become infected. Was it a handful? Dozens? Hundreds? As a result, the city's earliest data on COVID-19 was reported to the public with stunning simplicity, a grid with two organizing columns: New York City residents versus non-residents.

Now, around 30,000 New Yorkers get tested for COVID-19 every day, marking a huge improvement in capacity but whose turnaround time still needs to get faster. Still, the large volume of testing has inarguably saved lives, by giving government officials the ability to know where to apply resources, and exposing all too familiar healthcare inequities of race and class.

By most accounts, New York City has one of the best COVID-19 tracking websites, providing the public with a robust and detailed array of data and visualizations that officials continue to refine. As infection levels have come down, experts say that testing data has become an invaluable surveillance tool that can signal future outbreaks, as evidenced by the Department of Health's recent alerts about clusters in South Brooklyn and parts of central Queens.

So what can average New Yorkers glean from all of this? A lot actually. Transparency is one of the keys to fighting the disease and understanding how it is spreading helps everyone. Here is what you need to know about the most vital statistics.

Why is everyone so obsessed with the positivity rate? What exactly is this measuring and how much should I fixate on it?

New York officials have spent the summer crowing about the state and local test positivity rate, which has hovered around 1%. It's one of the key data points that Mayor Bill de Blasio recites everyday. A test positivity rate is often used interchangeably with the infection rate. What's important to keep in mind is that test positivity measures the share of people tested who are coming up positive for coronavirus, not the true proportion of confirmed cases in the population at large at a given point in time. That is typically referred to as the prevalence.

Test positivity is an important indicator. It is used to determine how widespread the virus is as well as whether testing is sufficient. Higher positivity rates suggest higher infection rates. But they also suggest that there are likely more people in the community who have COVID-19 but who have not yet been tested.

There's an important caveat, however, with positivity rates. Both de Blasio and Governor Andrew Cuomo release daily positivity rates for New York City and the state. That's the fraction of positive tests that come up in one day. But public health experts say it's best to look at sustained trends over one or two weeks, not merely one day's worth of data. As an example, data on tests performed Sunday is noted as being prone to a "day of week bias." Because more clinics are closed on that day, those who wish to get tested need to go to hospitals. But those people tend to be sicker.

Just this past Tuesday, the mayor reported that the city's daily positivity had soared to more than 3%. The sudden fluctuation prompted him to begin incorporating what every expert says is a more reliable indicator: the positivity rate calculated on a rolling seven-day average.

New York City's Department of Health tracks both the daily and average positivity rates on its website.

What about the other indicators that Mayor Bill de Blasio reads everyday?

In addition to the test positivity, the mayor announces two other "milestone" indicators that can also be found on the Department of Health's website: the seven-day average of new reported cases citywide and the number of people admitted to hospitals with covid-like illnesses, two basic barometers that show the spread of disease and how fast it's growing or slowing down over time. At the height of the outbreaks in New York City, there were over 6,300 people diagnosed with COVID-19 in one day. That number has since fallen to several hundred new cases in a day.

Aside from seeing how much the virus is straining the healthcare system, the number of hospitalizations also tells us how severe the disease currently is. There are some signs now in Europe, for example, that the coronavirus has lost its potency because of fewer hospitalizations despite a surge in new cases. The statistic is often called "a lagging indicator," meaning that a rise in hospitalizations will typically follow a surge in infections.

All of the milestone indicators can be found on the Department of Health's website. The page is updated daily but the numbers do get retroactively revised. Read on to learn why.

And Governor Andrew Cuomo? Isn't he the PowerPoint chart guru? What about his numbers?

Governor Andrew Cuomo during a press briefing in April.

Governor Andrew Cuomo / Flickr

During the crisis, Cuomo became famous for wielding his PowerPoint charts during his 96-day streak of daily press briefings. In those early months when New York was the epicenter of the pandemic, he focused on the data that communicated the urgency of the immediate situation: hospitalizations—total and new admissions, and ICU admissions—as well as deaths. Over time, as the state expanded testing, he began including testing benchmarks as well. That includes the number of total tests performed statewide and the daily positivity.

Like New York City, the state DOH has its own coronavirus tracking website where the public can view tests and positive cases broken down by county. Both departments do separate data collection and analysis using different methodologies, which will result in discrepancies in the numbers they report. In reporting positivity, for example, one of the biggest differences is the date each team uses. City health officials use the date the test was performed, whereas state officials will use the date the test was reported to them. According to Jonah Bruno, a state Department of Health spokesman, any facility performing coronavirus testing in New York state is required to report test results to the state's health department.

The city's positivity report is always on a lag because epidemiologists base their analysis on data that is two-days-old so as to give the numbers a chance to become more accurate. Rather than being set in stone, public health data is constantly being revised as more data become available or gets corrected.

"Data is always snapshots," Patrick Gallahue, a spokesman for the city's Department of Health explained. "What you know about yesterday today is a lot different than what you know about yesterday tomorrow."

No one method is considered right or wrong, said Corinne Thompson, a director of epidemiology with the New York City Department of Health. But she said the city prefers to use the date the test was performed because labs can often have delays in reporting results.

Dr. Jessica Justman, an epidemiologist at Columbia University, said that having two teams working independently on the data is an advantage to New Yorkers. "For really important numbers, you want this kind of validation," she said, adding that both the city and state health departments are considered excellent by those in the public health field.

I've been seeing a lot stories lately about "cluster" neighborhoods or "hotspots." What do these terms this mean?

A disease cluster is defined as multiple cases that may be grouped or linked together in place and time without consideration of the number of cases expected. It is related to an outbreak, which involves an often sudden increase in the number of cases that is beyond what is expected for a specific place.

Public health experts determine outbreaks by examining the presence of clusters. An outbreak is called an epidemic when there is a sudden increase in cases in a broader population area.

New York City health officials are currently referring to the "areas of concern" in Southern Brooklyn, Williamsburg, Central Queens and Far Rockaway as four "clusters." In a tweet on Friday, de Blasio referred to them as "cluster outbreaks."

Dr. Denis Nash, an epidemiologist at CUNY, said he considers the latest events outbreaks.

"What it sounds like is there’s been a jump in transmission in those neighborhoods and that’s an outbreak," he said.

Hotspot, a term often preferred by Governor Cuomo, is not a technical term. It is typically used to provide a comparative snapshot of where transmission is higher on any given day. Alternatively, a "coldspot" can refer to a place that is reporting relatively little transmission.

Nash said hotspot can also be used to single out neighborhoods where transmission is rising out of proportion with the rest of the city or state. Cuomo, for example, this week began releasing a list of daily positivities from 20 hotspot ZIP codes.

How will rises in the positivity rate or cases affect New York City's reopening?

Mayor de Blasio has set three basic warning thresholds that would trigger the city to reassess its reopening plan.

The mayor has also said that he would close public schools if the average positivity were to climb to 3%, and that individual schools would close if there were two or more unrelated cases in the building. He has also said he would reassess indoor dining, which resumed at 25% capacity this week, if the average positivity were to hit 2%.

Meanwhile, Governor Cuomo has laid out his own criteria for reopening, which can be found on the state's "early warning" dashboard.

Given the politically fraught nature of shutdowns, should outbreaks worsen in New York City, expect to see Cuomo and de Blasio clash over who gets to make the final decision.

I want to know how much COVID-19 is spreading in my neighborhood. Where can I go to find this out?

For neighborhood-level data, New York City residents should visit the health department's website that provides recent four week trends by ZIP code. Two maps allow users to toggle between cases and deaths, as well as a test positivity and test rate, for every neighborhood. At the bottom of each map is a link says "Get the data." That directs to a Github site that breaks down new cases by week and ZIP code.

The page is updated every Thursday.

And to follow citywide updates, keep reading Gothamist! Since January, we have been tracking the virus with our daily coronavirus updates live blog and statistics page, where we map cases, hospitalizations, deaths, and plot comparisons as well as our own forecast. And if you have a question about the pandemic or coronavirus, feel free to email us at [email protected].

Tagged

COVID-19

coronavirus

explainer

Elizabeth Kim

Elizabeth Kim is a reporter on the People and Power desk who covers mayoral power. She previously covered the pandemic, housing, redevelopment and public spaces. A native of Queens, she speaks fluent Mandarin. Got a tip? Email [email protected]

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Gothamist is funded by sponsors and member donations

Gothamist is funded by sponsors and member donations

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