The study is based on self-reported responses to “How many days do you generally consume breakfast in a typical week?” (in Chinese) ... it's an interesting ques

The study is based on self-reported responses to “How many days do you generally consume breakfast in a typical week?” (in Chinese) ... it's an interesting question that clearly must have a customary/social component. As an annoying pedant I'd be compelled to answer "every day" based on the definition of breakfast as the first meal of the day. I don't know how the term or the custom translates to coal miners of eastern Tangshan province, though.