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Sleep duration (hours; mean, standard deviation) in each of the four questionnaires
| Year of questionnaire | Men | Women | Age group 18–34 years |
Age group 35–54 years |
Age group 55+ years |
|---|---|---|---|---|---|
| 1975 | 7.57, 0.95 | 7.69, 0.98 | 7.69, 0.92 | 7.57, 0.93 | 7.52, 1.20 |
| 1981 | 7.53, 0.85 | 7.67, 0.89 | 7.63, 0.83 | 7.56, 0.84 | 7.64, 1.06 |
| 1990 | 7.39, 0.81 | 7.55, 0.84 | 7.53, 0.83 | 7.46, 0.83 | 7.50, 0.88 |
| 2011 | 7.39, 0.89 | 7.37, 0.86 | No data | 7.34, 0.84 | 7.38, 0.88 |
