"We see the same daily rhythm across seven days, which suggests something more fundamental going on, such as biological or circadian rhythms," Golder said. "We also saw the same basic pattern all across the globe. We are all human beings and subject to [the] same psychological factors, we're all refreshed by sleep, and this is something that is just part of us."
Sonja Lyubomirsky, a professor of psychology at University of California, Riverside, said the study innovatively used technology to monitor people's moods and "gets at some questions we wouldn't get at" by following millions of people.
However, while Twitter boasts about 175 million account users, that's still a small number worldwide, Lyubomirsky said, and isn't a representative sample of adults.
"It's very descriptive and a nice use of new methodology," she said, "but it's not revolutionary."
Golder agreed that study participants didn't represent a random sample, since Twitter users tend to be younger, highly educated and slightly more affluent.
"It's important to remember that even though the Internet is largely mainstream, large groups don't have access to it or use certain aspects of it," he said. "And we're only measuring what people tweet about . . . they're much more likely to tweet about making coffee than using the bathroom."
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SOURCES: Scott Golder, doctoral student, sociology, Cornell University, Ithaca, N.Y.; Sonja Lyubomirsky, Ph.D., professor, psychology, University
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