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Table 1 Demographic and sleep characteristics of study population presented as means and standard deviations

From: Associations of bedtime, sleep duration, and sleep quality with semen quality in males seeking fertility treatment: a preliminary study

DemographicTotalReduced semen qualityP-value
Mean (SD)(N = 104)No (N = 48)Yes (N = 56)
Age (years)34.00 (5.5)33.67 (5.1)34.30 (5.8)0.55
Education a3.57 (1.2)3.77 (1.1)3.39 (1.3)0.10
Income b3.90 (1.0)4.06 (0.9)3.77 (1.0)0.12
Tobacco smoking c0.06 (0.2)0.04 (0.2)0.07 (0.3)0.51
Alcohol consumption (standard drinks/week)6.86 (8.5)7.13 (10.1)6.63 (6.8)0.77
Bedtime (hour in 24-h format)22.72 (0.9)22.58 (0.8)22.86 (0.9)0.09
Sleep duration (hours/day)7.24 (0.9)7.42 (0.66)7.09 (1.0)0.05*
Global PSQI score8.17 (2.3)7.69 (1.9)8.59 (2.4)0.04*
  1. a (1) Unskilled – no further education after high school, (2) basic education, (3) technical education (e.g. hairdresser, carpenter, mechanic, chef, plumber), (4) professional Bachelor’s degree (e.g. nurse, teacher, social worker), and (5) Master’s degree at university level. b Household annual income of: (1) < 200.000 DKK, (2) 200.000–350.000 DKK, (3) 351.000–500.000 DKK, (4) 501.000–700.000 DKK, (5) > 700.000 DKK. c % of total with (0) not currently smoking, (1) currently smoking. SD: Standard deviation. N: Number of observations. PSQI: Pittsburgh Sleep Quality Index global score. P-value based on simple t-tests assuming unequal variance. * Significant at p < 0.05