Sleep-duration extension and midpoint displacement in United States adults: joint classification and survey measurement constraints

Abstract

Introduction: Duration extension and sleep-midpoint displacement can select different respondents despite a shared cutoff in hours. We examined their joint classification and the released timing/summary constraints, without claiming validation against biological phase or a new social-jet-lag concept.

Methods: An exploratory cross-sectional National Health and Nutrition Examination Survey (NHANES) 2017–2018 analysis used interview weights, strata and primary sampling units. Among adults aged at least 20, signed free-day minus workday main-period duration was cross-classified against absolute circular midpoint displacement. The primary inclusive cutoff was one hour, with declared secondary thresholds. Rounded-duration comparisons excluded grouped extremes; survey confidence intervals were pointwise 95% intervals.

Results: Of 5569 adult interviews, 5454 had complete valid timing, representing 98.6 (98.1–98.9)% weighted availability. At one hour, extension only, midpoint only and both comprised 10.7%, 17.2% and 28.8%. Discordance was 27.9 (26.1–29.7)%. The paired marginal difference was -6.5 (-8.5–-4.6) percentage points. Discordance remained 18.0% at two hours despite close marginal proportions. Within 5442 ordinary-summary records, six and five classifications changed after summary rounding at one and two hours, respectively; these rare estimates require reliability review.

Conclusion: Joint tables reveal construct-dependent selection obscured by marginal prevalences. Clock availability, grouped summaries and circular interval conventions constrain interpretation. These shared-source operational quantities do not establish true sleep debt, instrument superiority, biological circadian misalignment or clinical thresholds.

Keywords

• Sleep Duration
• Circadian Rhythm
• Nutrition Surveys
• Cross-Sectional Studies
• Surveys and Questionnaires