Table 1

Basic descriptive statistics of the UK Twins sample showing available sample size for each phenotype

Age, years225653.3953.0231.8873.808.19
Height, cm2256162.22162.00142.00182.005.77
Weight, kg225664.9363.0043.00128.0011.39
BMI, kg/m2225624.7423.9316.2351.394.24
Smoking, pack years13784.11007810.21
Manual work, years23083.0600467.55
Disc height*9043.7640152.68
Disc signal*9065.9260153.26
Disc bulge*9082.1920101.79
Anterior osteophytes*9031.4910131.99
LDD summary score89813.38120537.66
Hip BMD, g/cm251620.910.910.601.370.13
Lumbar spine BMD, g/cm29120.990.990.561.540.16
  • N is the sample size available for each phenotype.

  • * Summary trait score (0–3) over five intervertebral discs.

  • Summary score of the four trait scores.

  • BMD, body mineral density; BMI, body mass index; LDD, lumbar degenerative disc disease.