Opinion | Google Searches Can Help Us Find Emerging Covid-19 Outbreaks

Does the Google search data really mean that eye pain is a symptom of Covid-19? Not necessarily. There may be other reasons that people in these parts of the country are searching for eye pain. However, I tested alternative explanations that people suggested to me, and they did not fit the data. The searches do not seem to be driven by allergies; they are not related to pollen concentrations. Nor do they seem to be driven by people staying at home and staring at screens more; eye pain search rates do not correlate with data from cellphones that have measured recent reductions in movement.

It is hard to imagine that curiosity alone is driving the relationship between eye pain and Covid-19 prevalence rates. Other potential symptoms that have received extensive media attention don’t show nearly as strong a statewide relationship with Covid-19 prevalence rates.

There is also some evidence for eye pain as a symptom of Covid-19 from searches in other parts of the world. Notably, searches for eye pain rose above fourfold in Spain between the middle of February and the middle of March and rose about 50 percent in Iran in March. Eye pain searches seemingly haven’t risen in Italy, though that data is noisier. (To examine data across the world, I am using Google’s topic “eye pain,” which groups together many different searches in various languages related to the topic. Since Google reports different random samples of their data for different data requests, I have averaged a number of different samples.)

I think search data offers suggestive evidence that eye pain can be a symptom of the disease. However, it might only affect a small fraction of Covid-19 patients. Overall search volume for eye pain, despite rising substantially in Covid-19 hot spots, remains well below search volume for other symptoms. In New York there are now about one-sixth as many searches related to eye pain as there are searches related to loss of smell.

Nonetheless, doctors and public health officials should probably look closely at the relationship between Covid-19 and eye pain. If nothing else, we need to understand why there is frequently a large uptick in people telling Google that their eyes hurt when known cases of Covid-19 in a location rise to extremely high levels.

More people can study search trends around the world to help us learn about Covid-19. In 2006, Google released Google Trends, a public tool that the research community can use to study anonymous and aggregate search data. That is how I found everything I reported in this piece. It is plausible that important facts about the Covid-19 disease could be found here or in other large data sets by data scientists, medical experts or even amateur data sleuths.

Seth Stephens-Davidowitz (@SethS_D) is an economist, the author of “Everybody Lies: Big Data, New Data, and What the Internet Can Tell Us About Who We Really Are” and a contributing opinion writer.

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