R/builtin_references.R
builtin_references.RdA data frame containing the age-dependent distribution of the D-score for children aged 0-5 years. The distribution is modelled after the LMS distribution (Cole & Green, 1992) or BCT model (Stasinopoulos & Rigby, 2022) and is equal for both boys and girls. The LMS/BCT values can be used to graph reference charts and to calculate age-conditional Z-scores, also known as the Development-for-Age Z-score (DAZ).
builtin_referencesA data.frame with the following variables:
| Name | Label |
population | Name of the reference population |
key | D-score key, e.g., "dutch", "gcdg" or "gsed" |
distribution | Distribution family: "LMS" or "BCT" |
age | Decimal age in years |
mu | M-curve, median D-score, P50 |
sigma | S-curve, spread expressed as coefficient of variation |
nu | L-curve, the lambda coefficient of the LMS/BCT model for skewness |
tau | Kurtosis parameter in the BCT model |
P3 | P3 percentile |
P10 | P10 percentile |
P25 | P25 percentile |
P50 | P50 percentile |
P75 | P75 percentile |
P90 | P90 percentile |
P97 | P97 percentile |
SDM2 | -2SD centile |
SDM1 | -1SD centile |
SD0 | 0SD centile, median |
SDP1 | +1SD centile |
SDP2 | +2SD centile |
Here are more details on the reference population:
The "dutch" references were calculated from the SMOCC data, and cover
age range 0-2.5 years (van Buuren, 2014).
The "gcdg" references were calculated from the 15 cohorts of the
GCDG-study, and cover age range 0-5 years (Weber, 2019).
The "phase1" references were calculated from the GSED Phase 1 validation
data (GSED-BGD, GSED-PAK, GSED-TZA) cover age range 2w-3.5 years. The
age range 3.5-5 yrs is linearly extrapolated and are only indicative.
The "preliminary_standards" were calculated from the GSED Phase 1 validation
data (GSED-BGD, GSED-PAK, GSED-TZA) using a subset of children with
covariate indicating healthy development.
Cole TJ, Green PJ (1992). Smoothing reference centile curves: The LMS method and penalized likelihood. Statistics in Medicine, 11(10), 1305-1319.
Van Buuren S (2014). Growth charts of human development. Stat Methods Med Res, 23(4), 346-368. https://stefvanbuuren.name/publication/van-buuren-2014-gc/
Weber AM, Rubio-Codina M, Walker SP, van Buuren S, Eekhout I, Grantham-McGregor S, Caridad Araujo M, Chang SM, Fernald LCH, Hamadani JD, Hanlon A, Karam SM, Lozoff B, Ratsifandrihamanana L, Richter L, Black MM (2019). The D-score: a metric for interpreting the early development of infants and toddlers across global settings. BMJ Global Health, BMJ Global Health 4: e001724. https://gh.bmj.com/content/bmjgh/4/6/e001724.full.pdf
Stasinopoulos M, Rigby R (2022). gamlss.dist: Distributions for Generalized Additive Models for Location Scale and Shape, R package version 6.0-3, https://CRAN.R-project.org/package=gamlss.dist
# get an overview of available references per key
table(builtin_references$population, builtin_references$key)
#>
#> 293_0 dutch gcdg gsed1912 gsed2212 gsed2406
#> dutch 0 144 0 0 185 185
#> gcdg 0 0 121 121 0 0
#> phase1 186 0 0 0 186 186
#> preliminary_standards 0 0 0 0 0 185