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

Bird, Philippa K; McEachan, Rosemary R. C.; Mon-Williams, Mark; Small, Neil; West, Jane; Whincup, Peter; Wright, John; Andrews, Elizabeth; Barber, Sally E; Hill, Liam J B; Lennon, Laura; Mason, Dan; Shire, Katy A; Waiblinger, Dagmar; Waterman, Amanda H.; Lawlor, Deborah A.; Pickett, Kate E.

doi:10.1186/s12889-019-7222-2

BMC Public Health

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)	Number^a	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	Receipt of means tested benefits	Being bullied (all or some of the time)	3500	1.10
White British	Not managing financially	Child low wellbeing	3000	1.38
Pakistani	Not managing financially	Child low wellbeing	3500	1.36
For objective 2: healthy childhood growth, adiposity and cardiometabolic health in children and adults
Group	Exposure	Outcome (continuous)	Number^a	Minimal effect detectable^b
Group	Exposure	Outcome (continuous)	Number^a	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	Any maternal metabolite from NMR	Offspring tricep skinfolds at age 10	3500	0.07	0.10
White European	Gestational diabetes	Offspring systolic blood pressure at age 10	3400	0.11	0.16
South Asian	Gestational diabetes	Offspring systolic blood pressure at age 10	3850	0.08	0.10
White British	Cord-blood Epigenome wide DNA methylation^d	Offspring BMI at age 10	400	0.15	0.24
Pakistani	Cord-blood Epigenome wide DNA methylation^d	Offspring BMI at age 10	450	0.14	0.23
White European	Hypertensive disorder of pregnancy	Maternal predicted 10-year cardiovascular risk	3400	0.03	0.05
South Asian	Hypertensive disorder of pregnancy	Maternal predicted 10-year cardiovascular risk	3850	0.03	0.06
For objective 3: Determinants of child cognitive and motor development at age 7–11
Study / group	Exposure	Outcome (binary)	Number^a	Minimal effect detectable (RR)^c P = 0.05
White British	Not managing financially	Educational problems	3000	1.23
Pakistani	Not managing financially	Educational problems	3500	1.22
White British	No safe place to play (at baseline)	Motor development delay	3000	1.52
Pakistani	No safe place to play (at baseline)	Motor development delay	3500	1.37
Study / group	Exposure	Outcome (continuous)	Number^a	Minimal effect detectable^b
Study / group	Exposure	Outcome (continuous)	Number^a	P = 0.01	P = 0.0001
White British	Overall Behavioural Difficulties	Motor Skills Test Battery Score	3000	0.10	0.14
Pakistani	Overall Behavioural Difficulties	Motor Skills Test Battery Score	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	Specific Difficulties with Externalising Behaviours	Assessment of Sustained Attention (visuo-motor tracking)	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	Specific Difficulties with Internalising Behaviours	Assessment of Executive Planning (timed maze tracing)	3500	0.17	0.23

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

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ISSN: 1471-2458

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