sitar (version 1.1.0)

cLMS: LMS conversion to and from z-scores

Description

Routines to handle references constructed with the LMS method. Given a set of LMS values, the functions convert z-scores to measurement centiles and vice versa.

Usage

cLMS(z, L = 1, M, S)
zLMS(x, L = 1, M, S)

Arguments

z

vector or one-column matrix of z-scores to be converted to measurements.

L

vector of Box-Cox transformation (lambda) values, L in the LMS method.

M

vector of medians (mu), M in the LMS method.

S

vector of coefficients of variation (sigma), S in the LMS method.

x

vector or one-column matrix of measurements to be converted to z-scores.

Value

If x and z are vectors zLMS and cLMS each return a vector, respectively of z-scores and measurement centiles, with length matching the length of (the longest of) x or z, L, M and S. If x or z are matrices zLMS and cLMS each return a matrix, the number of rows matching the length of (the longest of) L, M and S, and the number of columns matching the length of x or z.

Details

L, M and S -- and if vectors then x and z -- should all be the same length, recycled if necessary. The formulae converting x to z and vice versa are: $$z = \frac{(x/M)^L - 1}{L S}$$

$$x = M (1 + L S z)^{1/L})$$ where L is reset to 10^-7 if it is zero. The LMS method is the same as the BCCG family in the gamlss package, except that lambda in LMS is referred to as nu in BCCG.

See Also

z2cent, LMS2z, pdLMS

Examples

# NOT RUN {
cLMS(z = as.matrix(-2:2), L = 1:-1, M = 5:7, S = rep(0.1, 3))
cLMS(z = 0:2, L = 1:-1, M = 7, S = 0.1)
cLMS(z = as.matrix(0:2), L = 1:-1, M = 7, S = 0.1)
zLMS(x = 6.5, L = 1:-1, M = 5:7, S = rep(0.1, 3))

# }