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Table 1 Sample demographics by each cohort group and wave

From: The CogBIAS longitudinal study of adolescence: cohort profile and stability and change in measures across three waves

Wave 1
 CohortTotalX1X2X3X4X5X6X7X8X9X10
N5041530624713341191045426
Mean Age (SD)13.4 (.7)12.6 (.4)11.7 (.3)13.4 (.3)13.4 (.3)12.2 (.4)12.8 (.3)14.0 (.4)13.1 (.3)14.3 (.3)13.2 (.3)
Year group7–97–87887–889898
Gender (% Female)55%40%50%100%100%100%47%0%100%0%58%
Ethnicity (% Caucasian)75%60%87%68%72%69%59%86%69%76%85%
SES (Median, IQR)4 (2)4 (2)3 (2)4 (2)3 (2)4 (2)2 (2)4 (1)4 (2)4 (2)3 (2)
Wave 2
 CohortTotalX1X2X3X4X5X6X7X8X9X10
N45092560406261091015024
Mean Age (SD)14.5 (.6)14.0 (.4)13.3 (.3)14.5 (.3)14.8 (.3)13.5 (.2)14.0 (.3)15.1 (.4)14.1 (.3)15.4 (.3)14.3 (.3)
Year group8–108–999108–99109109
Gender (% Female)56%56%52%100%100%100%42%0%100%0%58%
Ethnicity (% Caucasian)75%56%84%67%73%67%65%86%69%74%42%
SES (Median, IQR)4 (2)4 (2)3 (2)4 (2)3 (2)4 (2)2 (2)4 (1)4 (2)4 (2)3 (2)
Wave 3
 CohortTotalX1X2X3X4X5X6X7X8X9X10
N4118226237121292925024
Mean Age (SD)15.7 (.6)15.3 (.4)14.8 (.3)15.9 (.3)15.8 (.3)14.5 (.4)15.0 (.3)16.0 (.4)15.4 (.3)16.1 (.3)15.3 (.3)
Year group9–1110–111011119–101111111110
Gender (% Female)58%50%46%100%100%100%67%0%100%0%58%
Ethnicity (% Caucasian)76%63%86%68%73%75%75%85%70%74%88%
SES (Median, IQR)4 (2)4 (2)3 (2)4 (2)3(2)4 (2)2 (2)4 (1)4 (2)4 (2)3 (2)
  1. Note: Update from the protocol paper (Booth et al., 2017); age has now been coded to two decimal places, and SES (Socio-Economic Status) is the median of both mother and father education level; SD Standard Deviation; IQR Interquartile Range; 11% attrition at Wave 2 and 19% attrition by Wave 3