Calculate Development-for-Age Z-score (DAZ)

The daz() function calculated the Development-for-Age Z-score (DAZ). The DAZ represents a child's D-score after adjusting for age by an external age-conditional reference.

daz(d, x, reference_table = NULL, dec = 3, verbose = FALSE)

zad(z, x, reference_table = NULL, dec = 2, verbose = FALSE)

Arguments

d: Vector of D-scores
x: Vector of ages (decimal age)
reference_table: A data.frame with the LMS or BCT reference values. The default NULL selects the default reference belonging to the key, as specified in the base_population field in dscore::builtin_keys.
dec: The number of decimals (default dec = 3).
verbose: Print out the used reference table (default verbose = FALSE).
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

The zad() is the inverse of daz(): Given age and the Z-score, it finds the raw D-score.

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.

Author

Stef van Buuren

Examples

# using default reference and key
daz(d = c(35, 50), x = c(0.5, 1.0))
#> [1] 0.499 0.218

# print out names of the used reference table
daz(d = c(35, 50), x = c(0.5, 1.0), verbose = TRUE)
#> key:         gsed2406 
#> population:  preliminary_standards 
#> [1] 0.499 0.218

# using the default reference in key gcdg
reftab <- get_reference(key = "gcdg")
daz(d = c(35, 50), x = c(0.5, 1.0), reference_table = reftab)
#> [1] -0.425  0.299

# using Dutch reference in default key
reftab <- get_reference(population = "dutch", verbose = TRUE)
#> key:         gsed2406 
#> population:  dutch 
daz(d = c(35, 50), x = c(0.5, 1.0), reference_table = reftab)
#> [1] 1.709 0.996
# population median at ages 0.5, 1 and 2 years, default reference
zad(z = rep(0, 3), x = c(0.5, 1, 2))
#> [1] 33.39 49.29 65.33

# population median at ages 0.5, 1 and 2 years, gcdg key
reftab <- get_reference(key = "gcdg", verbose = TRUE)
#> key:         gcdg 
#> population:  gcdg 
zad(z = rep(0, 3), x = c(0.5, 1, 2), reference_table = reftab)
#> [1] 36.32 49.11 62.67

# population median at ages 0.5, 1 and 2 years, dutch key
reftab <- get_reference(key = "dutch", verbose = TRUE)
#> key:         dutch 
#> population:  dutch 
zad(z = rep(0, 3), x = c(0.5, 1, 2), reference = reftab)
#> [1] 35.27 48.91 63.77