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Table 6 Association between principal component 3 and pack-year category

From: Association of cytokine and matrix metalloproteinase profiles with disease activity and function in ankylosing spondylitis

Variable 0 pack years (n= 61 1 to 15 pack years (n= 37) 16 to 30 pack years (n= 17) > 30 pack years (n= 14) P(trend)a
PC3 -0.10 (1.80) 0.38 (1.17) 0.79 (1.21) 1.86 (2.51) < 0.0005
  1. Mean (standard deviation) values are shown. PC, principal component. aLinear test for trend.