Like most mass-media writeups of scientific studies, there's no science here. The sample size is absolutely tiny, and it's poorly designed on top of that.
Here are some problems with it:
- The sample size is absolutely insignificant. For studies that we want to generalize to all humans, a sample of at least 100,000 is ideal.
- This is not longitudinal or experimental data. We have no idea if we're just seeing a random correlation or not. There are simply too many variables to control for, especially with such a small population.
- Only people 47 to 59 were studied, and the questionnaire was administered in the present. We don't know what their sleep patterns have been in the past.
- The groups were self-reported, which likely caused problems. What if you're a morning person on weekdays, but not on weekends?
- Correlated health issues, like obesity or diabetes, might be the cause rather than the effect.
- They're presumably all Korean. I don't know how this might influence the study, but it very well might.
Here are some problems with it:
- The sample size is absolutely insignificant. For studies that we want to generalize to all humans, a sample of at least 100,000 is ideal.
- This is not longitudinal or experimental data. We have no idea if we're just seeing a random correlation or not. There are simply too many variables to control for, especially with such a small population.
- Only people 47 to 59 were studied, and the questionnaire was administered in the present. We don't know what their sleep patterns have been in the past.
- The groups were self-reported, which likely caused problems. What if you're a morning person on weekdays, but not on weekends?
- Correlated health issues, like obesity or diabetes, might be the cause rather than the effect.
- They're presumably all Korean. I don't know how this might influence the study, but it very well might.