By Elaine Nsoesie

Think of the last time you had food poisoning. Did you tweet about it? Did you Google your symptoms? Or did you write an angry review on Yelp?

Every day, people use the internet to seek and share health information. This opens up exciting new ways for scientists to study the health of a population, an approach known as digital epidemiology.

But, in most cases, we do not know much about the individuals who post this information. We don’t know if the data include people from poor households, or how the data break down according to race, gender or age group. We also don’t know if they include those who are most vulnerable to the disease of interest in a particular study.

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