D-score standard deviation score: DAZ

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 = as.numeric(names(d)), reference = get_reference(), dec = 3)

zad(z, x = as.numeric(names(z)), reference = get_reference(), dec = 2)

Arguments

d	Vector of D-scores
x	Vector of ages (decimal age)
reference	A `data.frame` with the LMS reference values. The default uses the `get_reference()` function. This selects a subset of rows from the `builtin_references` using its default `pop` argument.
dec	The number of decimals (default `dec = 3`).
z	Vector of standard deviation scores (DAZ)

Value

The daz() function return a named vector with Z-scores with length(d) elements

The zad() function returns a vector with D-scores with length(z) elements.

References

Cole TJ, Green PJ (1992). Smoothing reference centile curves: The LMS method and penalized likelihood. Statistics in Medicine, 11(10), 1305-1319.

Author

Stef van Buuren 2020

Examples

# using gcdg-reference
daz(d = c(35, 50), x = c(0.5, 1.0))
#>    0.5      1 
#> -0.425  0.299 

# using Dutch reference
daz(d = c(35, 50), x = c(0.5, 1.0), reference = get_reference("dutch"))
#>    0.5      1 
#> -0.091  0.357 
# population median at ages 0.5, 1 and 2 years, gcdg reference
zad(z = rep(0, 3), x = c(0.5, 1, 2))
#>   0.5     1     2 
#> 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"))
#>   0.5     1     2 
#> 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"
)