Descriptive statistics.

<p><i>Note.</i> M = Mean; SD = standard deviation.</p><p>*participants who completed all four tests.</p><p>Descriptive statistics.</p

Multivariate model fitting results for the three music aptitude measures (Pitch, Rhythm, and Melody) and WMT (last) corrected for age and sex with the best fitting models highlighted in bold.

<p>Note: A = additive genetic; C = common/shared environmental; E = non-shared environmental.</p><p>*E cross-paths are removed from the model.</p><p>Note that the independent model and the Cholesky decomposition are not nested and therefore cannot be directly compared.</p><p>Multivariate model fitting results for the three music aptitude measures (Pitch, Rhythm, and Melody) and WMT (last) corrected for age and sex with the best fitting models highlighted in bold.</p

Different models applied to the data.

<p>(A) Cholesky decomposition. (B) Independent pathway model with two common genetic factors. (C) Independent pathway model with one common genetic factor. A = additive genetic influences. Subscripts <i>c</i> and <i>s</i> denote common and specific influences, respectively. Genetic factors of the Cholesky decomposition are labelled A1, A2, A3, and A4.</p

Associations between sleep problems and the occurrence of gastroesophageal reflux disease (GERD), among 365 dyzygotic (DZ) twin pairs discordant for GERD.

<p>OR, Odds ratio; CI, confidence intervals.</p><p><i>^a</i>ORs adjusted for educational level, body mass index, and tobacco smoking. Genetic and early environmental factors, sex and age are adjusted for by the within pair structure.</p><p><i>^b</i>The insomnia index was constructed by combining the three different sleep problem questions and 0 points were given for “seldom”, 1 point for “sometimes” and 2 points for “often”. The highest scores, 4–6 points or if the participant had answered “often”, were then classified as “often having sleep problems”, 1–3 points as “sometimes having sleep problems” and 0 as ”seldom having sleep problems”.</p

The distribution of gastroesophageal reflux disease (GERD) in same-sexed dizygotic (DZ) and monozygotic (MZ) twin pairs.

a<p>One twin has GERD, and the other not.</p

Twin cross-trait correlations of sleep problems and gastroesophageal reflux disease.

a<p>Polychoric correlation.</p>b<p>Asymptotic error of the polychoric correlations.</p><p><i>^c</i>The insomnia index was constructed by combining the three different sleep problem questions and 0 points were given for “seldom”, 1 point for “sometimes” and 2 points for “often”. The highest scores, 4–6 points or if the participant had answered “often”, were then classified as “often having sleep problems”, 1–3 points as “sometimes having sleep problems” and 0 as ”seldom having sleep problems”.</p

Associations between sleep problems and the occurrence of gastroesophageal reflux disease (GERD) among 7,857 twins.

<p>OR, odds ratio; CI, confidence interval.</p>a<p>The different numbers of GERD cases for the four sleep exposures are due to different numbers of missing observations in the sleep questions.</p>b<p>ORs adjusted for age, sex, educational level, body mass index, and tobacco smoking.</p>c<p>The insomnia index was constructed by combining the three different sleep problem questions and 0 points were given for “seldom”, 1 point for “sometimes” and 2 points for “often”. The highest scores, 4–6 points or if the participant had answered “often”, were then classified as “often having sleep problems”, 1–3 points as “sometimes having sleep problems” and 0 as ”seldom having sleep problems”.</p