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Table 1 Comparison of student and school-level characteristics between samples

From: Sources of potential bias when combining routine data linkage and a national survey of secondary school-aged children: a record linkage study

   School consented to data linkage question  
  Full SHW survey sample (n = 103,971; schools = 193) Data linkage sub-sample (n = 18,956; schools = 39) Data linkage control sample (n = 8374; schools = 22)a Regression-based P-value (data linkage vs. non-data linkage sample)b
  n (%) n (%) n (%)  
Student-level
 Gender
  Male 50,452 (48.5) 9545 (50.4) 3788 (45.2) 0.078
  Female 51,458 (49.5) 9064 (47.8) 4421 (52.8) 0.110
  Did not want to answer 2061 (2.0) 347 (1.8) 165 (2.0) 0.283
 School grade
  Year 7 22,634 (21.8) 3787 (20.0) 2064 (24.7) 0.005
  Year 8 22,421 (21.6) 4122 (21.8) 1998 (23.9) 0.755
  Year 9 22,208 (21.4) 4347 (22.9) 1628 (19.4) 0.023
  Year 10 19,704 (19.0) 3500 (18.5) 1417 (16.9) 0.580
  Year 11 17,004 (16.4) 3200 (16.9) 1267 (15.1) 0.552
 Weekly cigarette smoker
  No 96,170 (96.6) 17,656 (96.9) 7745 (96.4)
  Yes 3422 (3.4) 571 (3.1) 291 (3.6) 0.168
 cannabis use
  No 94,156 (95.6) 17,799 (96.2) 7604 (95.5)
  Yes 4305 (4.4) 699 (3.8) 357 (4.5) 0.061
 Ever truant
  No 68,071 (73.9) 13,666 (75.4) 5457 (73.2)
  Yes 23,989 (26.1) 4455 (24.6) 1995 (26.8) 0.046
 Ever excluded
  No 86,614 (92.2) 17,216 (93.0) 6947 (91.1)
  Yes 7370 (7.8) 1304 (7.0) 675 (8.9) 0.091
SWEMWBS (sd.) 21.955 (4.51) 22.094 (4.33) 21.867 (4.40) 0.048
FAS (sd.) 9.28 (2.34) 9.333 (2.32) 9.166 (2.34) 0.557
School-level
 Mean FAS (sd.) 9.309 (0.63) 9.353 (0.50) 9.192 (0.653) 0.595
  1. Notes: SWEMWBS, Short Warwick-Edinburgh Mental Wellbeing Scale; FAS, Family Affluence Scale
  2. aThe data linkage control sample refers to the 22/64 schools which consented to data linkage, but which were not randomly assigned to the data linkage sample following the 2:1 randomization process (see Fig. 1)
  3. bVariation in student socio-demographics and risk behaviours between samples were explored using binary and linear regression models (depending on the outcome variable) with adjustment for clustering by school. As the data linkage sample was nested within the full SHW survey sample, reported p-values were drawn from models comparing students attending data linkage (n = 39) versus non-data linkage (n = 154) schools
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