SITAR growth curve analysis - a statistical method to assess longitudinal growth and development data

Lead Research Organisation: University College London
Department Name: Institute of Child Health

Abstract

The pattern of growth in individual children, as represented by their growth curve of successive measurements (e.g. weight or height) plotted against age, may be informative about their circumstances at earlier ages, or conversely it may predict their risk of disease later in life, for example heart disease, stroke or type 2 diabetes. To investigate this it is useful to summarise the shape of each individual's growth curve in a simple way, so that its shape can be related to their earlier or later experiences. The SITAR method of growth curve analysis is a recently developed approach that does just this - it summarises each individual growth curve as just three numbers, reflecting respectively their size (i.e. whether they are tall or short, or heavy or light, as compared to others), their growth tempo (i.e. whether they are relatively mature or delayed in their timing of growth, e.g. when girls reach menarche), and velocity (how fast they are growing compared to others, e.g. in puberty). So for example an individual might be relatively tall, with early puberty, and growing relatively fast. In addition SITAR estimates a smooth average growth curve against which each individual's growth pattern can be compared. The surprising thing is that this model explains nearly all of the variability in growth between individuals, so that their size, tempo and velocity can be viewed as a complete summary of their growth pattern. Put another way, when adjusted for size, tempo and velocity all their growth curves look the same (the SITAR acronym mean Super-Imposition by Translation And Rotation). It is then simple to relate the values of size, tempo and velocity in individuals to their earlier or later experiences, and to look for links with their growth pattern.

Technical Summary

The SITAR method of growth curve analysis summarises individual growth patterns of e.g height or weight in three parameters (size, tempo and velocity) that are estimated as subject-specific random effects, plus a cubic spline estimate of the average growth curve. It explains over 95% of the age-specific variance in the outcome measure, and as such is an effective summary of individual growth patterns. The subject-specific random effects can then be related to earlier growth-affecting exposures or later health outcomes. Thus it is relevant in translational medicine and life course epidemiology. The aims of the project are (i) to further develop the SITAR methodology, (ii) to apply it to a series of existing growth studies, and (iii) to develop an existing SITAR software library in the R statistical language for its wider dissemination. Methodological developments will include applying the method to developmental as well as growth outcomes, and allowing the fitting of multiple mean curves rather than just one. The application studies are collaborations involving longitudinal data covering height, weight, spirometry and brain growth in childhood and puberty. The R library allows other statisticians and epidemiologists to apply the method relatively simply.

Planned Impact

Who will benefit from this research, and how?

o Academia
All researchers, national and international, interested in the analysis of longitudinal growth will find SITAR of interest, as it will allow them to summarise individual growth patterns in a simple way and then link the pattern to other aspects of the individual's health and lifestyle.

o Public Sector
National policy makers concerned with the high and rising levels of childhood obesity will want to explore the idea from SITAR that overweight children have an advanced maturational age, and look for lifestyle interventions that might counteract this accelerated age pattern.

o Business/Industry
The international pharmaceutical industry will value a statistical tool that simplifies and sharpens the assessment of growth-affecting treatments. SITAR's efficient use of data will mean that clinical trials involving growth outcomes need not be as large as before, and hence may reach conclusions more quickly and certainly more cheaply. This in turn should make cheaper the development of new growth-affecting drugs.

o Parents and children
Parents and children worldwide will benefit from improved growth assessment through the development of more effective evidence-based growth charts, particularly in puberty.

Publications

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Cole T (2017) The remarkable life of Frances Wood in Significance

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Cole TJ (2017) Statistics Notes: What is a percentage difference? in BMJ (Clinical research ed.)

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Cole TJ (2015) Too many digits: the presentation of numerical data. in Archives of disease in childhood

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Cole TJ (2018) Fifty years of child height and weight in Japan and South Korea: Contrasting secular trend patterns analyzed by SITAR. in American journal of human biology : the official journal of the Human Biology Council

 
Description US CDC BMI chart consultation
Geographic Reach North America 
Policy Influence Type Participation in a advisory committee
 
Description MRC Research Grant
Amount £72,596 (GBP)
Funding ID MR/M012069/1 
Organisation Medical Research Council (MRC) 
Sector Academic/University
Country United Kingdom
Start 03/2015 
End 02/2018
 
Description MRC research grant
Amount £120,518 (GBP)
Funding ID MR/R010692/1 
Organisation Medical Research Council (MRC) 
Sector Academic/University
Country United Kingdom
Start 03/2018 
End 08/2019
 
Title sitar library 
Description a library package written in R to fit my sitar growth curve model. It is available free to download from CRAN (the Comprehensive R Archive Network) and the source code is available free at Github (URL below). 
Type Of Material Computer model/algorithm 
Year Produced 2013 
Provided To Others? Yes  
Impact The sitar package has been used by several research groups who have downloaded it from CRAN. The sitar model has been the basis for my research for the past few years, and it has resulted in 19 publications and 78 citations (as of March 2019). 
URL https://github.com/statist7/sitar
 
Description Charlotte Wright 
Organisation University of Glasgow
Department Maternal and Child Health Glasgow
Country United Kingdom 
Sector Academic/University 
PI Contribution data and statistical analysis
Collaborator Contribution clinical expertise
Impact 26883079 29998577
Start Year 2011
 
Description Crozier 
Organisation University of Southampton
Department MRC Lifecourse Epidemiology Unit
Country United Kingdom 
Sector Public 
PI Contribution advice on growth modelling
Collaborator Contribution provision of data and shared authorship
Impact 30719940
Start Year 2011
 
Description MRC LHA 
Organisation University College London
Department MRC Unit for Lifelong Health and Ageing
Country United Kingdom 
Sector Public 
PI Contribution advice on growth and statistical analysis
Collaborator Contribution provision of data and other analyss
Impact publications: 27466311 27401728
Start Year 2013
 
Description MRC Nutrition ICH 
Organisation University College London
Department Institute of Child Health
Country United Kingdom 
Sector Academic/University 
PI Contribution advice on aspects of growth and statistical analysis
Collaborator Contribution provision of data and joint authorship
Impact publications: 17429924 17667912 18239656 16770333 16894361 17179023 17209191 23076617 22580078 27604768
 
Description Portex 
Organisation University College London
Department Institute of Child Health
Country United Kingdom 
Sector Academic/University 
PI Contribution advice on growth and statistical analysis
Collaborator Contribution provision of data and joint authorship
Impact publications: 19574442 19065626 17197485 18006882 20351026 20817707 23045209 22743675 22474159 22183491 25254426 25700391 25837028 26493801 27831907
 
Description Soc Med Bristol 
Organisation University of Bristol
Department School of Social and Community Medicine
Country United Kingdom 
Sector Academic/University 
PI Contribution advice on growth and statistical analysis
Collaborator Contribution provision of data and joint authorship
Impact publications: 16344844 16720666
 
Description US CDC 
Organisation Centers for Disease Control and Prevention (CDC)
Country United States 
Sector Public 
PI Contribution advice on growth and statistical analysis
Collaborator Contribution joint authorship
Impact publication: 17591624
 
Title sitar library 
Description Software to fit the SITAR method to growth curves, submitted as the sitar package to the Comprehensive R Archive Network (CRAN). 
Type Of Technology Software 
Year Produced 2013 
Open Source License? Yes  
Impact The availability of the open source software within R, the widely used free statistical software environment, has simplified its dissemination and encouraged others to try the method out. 
URL http://cran.r-project.org/web/packages/sitar/index.html
 
Description BBC Radio 4 More or Less 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Type Of Presentation Keynote/Invited Speaker
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact In 2011 I spoke on the BBC Radio 4 programme More or Less, two successive weeks, about predicting a child's adult height from their current height.

In 2013 I discussed a new index that had been proposed by Professor Trefethen to improve on the body mass index.

In 2015 I was asked the question "Are tall people more likely to get cancer?" (URL below)

Several friends and colleagues remarked that they'd heard the programme.
Year(s) Of Engagement Activity 2011,2013,2015
URL http://www.bbc.co.uk/programmes/p0343hhk
 
Description Dental age assessment furore 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact MP David Davies proposed using dental age assessment on child migrants to the UK. I was interviewed by BBC 5 Live, BBC News, Sky News and New Scientist to say that the assessment was inaccurate and should not be used.The Government stated at the time and subsequently that they would not use dental age assessment.
Year(s) Of Engagement Activity 2016
URL https://www.newscientist.com/article/2109703-dental-checks-cant-verify-the-age-of-child-asylum-seeke...
 
Description Interview for Newshour 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact A 5-minute interview with Lyce Douset on the BBC World Service Newshour radio programme about the proposal by the German CSU party to introduce dental age assessment for asylum seekers The interview runs from 40-45 minutes on the URL.
Year(s) Of Engagement Activity 2017
URL http://www.bbc.co.uk/programmes/w172vr1jvxkjn7n
 
Description Slimboy Fat - the problem with BMI 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact A radio programme introduced by Dr Mark Porter entitled "Slimboy Fat - the problem with BMI", where I discussed the pros and cons on the BMI.
Year(s) Of Engagement Activity 2015
URL http://www.bbc.co.uk/programmes/b064z553
 
Description Sun story on tallest couple 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact An article about the height of twins of a very tall couple. The article was accompanied by a commentary by me.
Year(s) Of Engagement Activity 2017
URL https://www.thesun.co.uk/living/3071810/britains-tallest-couple-add-twin-boys-to-their-lofty-brood-w...
 
Description Swedish TV programme on age assessment 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Malin Attefall edits and produces the weekly science programme Vetenskapens värld at SVT television in Sweden. She included interviews and film of me in a programme about developmental age assessment of child migrants that screened in October 2016. The programme was in Swedish, with some interviews in English (including mine). I understand that the programme generated some discussion within Sweden about the problems of assessing age in migrants.
Year(s) Of Engagement Activity 2016