The daz() function calculated the
"Development for Age Z-score".
The DAZ represents a child's D-score after adjusting
for age by an external age-conditional reference.
The zad() is the inverse of daz(): Given age and
the Z-score, it finds the raw D-score.
daz(d, x, reference = get_reference(), dec = 3)
zad(z, x, reference = get_reference(), dec = 2)Arguments
- d
Vector of D-scores
- x
Vector of ages (decimal age)
- reference
A
data.framewith the LMS reference values. The default uses theget_reference()function. This selects a subset of rows from thebuiltin_references.- dec
The number of decimals (default
dec = 3).- z
Vector of standard deviation scores (DAZ)
Value
Unnamed numeric vector with Z-scores of length length(d).
Unnamed numeric vector with D-scores of length length(z).
Details
Note 1: The Box-Cox Cole and Green (BCCG) and Box-Cox t (BCT)
distributions model only positive D-score values. To increase
robustness, the daz() and zad() functions will round up any
D-scores lower than 1.0 to 1.0.
Note 2: The daz() and zad() function call modified version of the
pBCT() and qBCT() functions from gamlss for better handling
of NA's and rounding.
References
Cole TJ, Green PJ (1992). Smoothing reference centile curves: The LMS method and penalized likelihood. Statistics in Medicine, 11(10), 1305-1319.
See also
Examples
# using GSED Phase 1 reference
daz(d = c(35, 50), x = c(0.5, 1.0))
#> [1] 0.788 0.587
# using Dutch reference
daz(d = c(35, 50), x = c(0.5, 1.0), reference = get_reference("gcdg"))
#> [1] -0.425 0.299
# using Dutch reference
daz(d = c(35, 50), x = c(0.5, 1.0), reference = get_reference("dutch"))
#> [1] -0.091 0.357
# population median at ages 0.5, 1 and 2 years, phase1 reference
zad(z = rep(0, 3), x = c(0.5, 1, 2))
#> [1] 32.28 47.93 64.30
# population median at ages 0.5, 1 and 2 years, gcdg reference
zad(z = rep(0, 3), x = c(0.5, 1, 2), reference = get_reference("gcdg"))
#> [1] 36.32 49.11 62.67
# population median at ages 0.5, 1 and 2 years, dutch reference
zad(z = rep(0, 3), x = c(0.5, 1, 2), reference = get_reference("dutch"))
#> [1] 35.27 48.91 63.77
# percentiles of D-score reference
g <- expand.grid(age = seq(0.1, 2, 0.1), p = c(0.1, 0.5, 0.9))
d <- zad(z = qnorm(g$p), x = g$age)
matplot(
x = matrix(g$age, ncol = 3), y = matrix(d, ncol = 3), type = "l",
lty = 1, col = "blue", xlab = "Age (years)", ylab = "D-score"
)
