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Table 2 Example power calculations for study objectives

From: Growing up in Bradford: protocol for the age 7–11 follow up of the Born in Bradford birth cohort

For objective 1: child social and emotional wellbeing at age 7–11
Group Exposure Outcome (binary) Numbera Minimal effect detectable (RR)c P = 0.05
White British Receipt of means tested benefits Being bullied (all or some of the time) 3000 1.11
Pakistani 3500 1.10
White British Not managing financially Child low wellbeing 3000 1.38
Pakistani 3500 1.36
For objective 2: healthy childhood growth, adiposity and cardiometabolic health in children and adults
Group Exposure Outcome (continuous) Numbera Minimal effect detectableb
P = 0.01 P = 0.0001
White British Any maternal metabolite from NMR Offspring tricep skinfolds at age 10 3000 0.06 0.09
Pakistani 3500 0.07 0.10
White European Gestational diabetes Offspring systolic blood pressure at age 10 3400 0.11 0.16
South Asian 3850 0.08 0.10
White British Cord-blood Epigenome wide DNA methylationd Offspring BMI at age 10 400 0.15 0.24
Pakistani 450 0.14 0.23
White European Hypertensive disorder of pregnancy Maternal predicted 10-year cardiovascular risk 3400 0.03 0.05
South Asian 3850 0.03 0.06
For objective 3: Determinants of child cognitive and motor development at age 7–11
Study / group Exposure Outcome (binary) Numbera Minimal effect detectable (RR)c P = 0.05
White British Not managing financially Educational problems 3000 1.23
Pakistani 3500 1.22
White British No safe place to play (at baseline) Motor development delay 3000 1.52
Pakistani 3500 1.37
Study / group Exposure Outcome (continuous) Numbera Minimal effect detectableb
P = 0.01 P = 0.0001
White British Overall Behavioural Difficulties Motor Skills Test Battery Score 3000 0.10 0.14
Pakistani 3500 0.11 0.16
White British Specific Difficulties with Externalising Behaviours Assessment of Sustained Attention (visuo-motor tracking) 3000 0.11 0.15
Pakistani 3500 0.11 0.15
White British Specific Difficulties with Internalising Behaviours Assessment of Executive Planning (timed maze tracing) 3000 0.09 0.12
Pakistani 3500 0.17 0.23
  1. a Numbers are all conservative; b minimal difference in outcome (SD units) per 1SD or 1 category of exposure that can be detected with this sample size; c Minimum Risk Ratio detectable for this sample size at p = 0.05. Power set to 85% in all of these estimates