sitar (version 1.4.0)

iotf: IOTF international body mass index reference

Description

The IOTF (International Obesity TaskForce) BMI growth reference (Cole and Lobstein 2012), fitted by the LMS method and summarised by values of L, M and S by sex and postnatal age from 2 to 18 years.

Usage

iotf

Format

A tibble with 66 observations on the following 5 variables:

years

numeric vector - postnatal age in years

L.bmi

numeric vector

M.bmi

numeric vector

S.bmi

numeric vector

sex

two-level factor with level 1 male and level 2 female

Details

The IOTF cutoffs for overweight and obesity (and also thinness) (see Cole et al 2000, 2007) can be obtained from this BMI reference. See the example for how to convert between cutoffs and z-scores.

The L, M and S values for each measurement correspond respectively to the Box-Cox power, median and coefficient of variation of the distribution by age and sex (Cole & Green 1992). The measurement short name and units for LMS2z are bmi (kg/m2).

References

Cole TJ, Green PJ. Smoothing reference centile curves: the LMS method and penalized likelihood. Stat Med 1992;11:1305-19.

Cole TJ, Bellizzi MC, Flegal KM, Dietz WH. Establishing a standard definition for child overweight and obesity worldwide: international survey. BMJ 2000;320:1240-3.

Cole TJ, Flegal KM, Nicholls D, Jackson AA. Body mass index cut offs to define thinness in children and adolescents: international survey. BMJ 2007;335:194-7.

Cole TJ, Lobstein T. Extended international (IOTF) body mass index cut-offs for thinness, overweight and obesity. Ped Obes 2012;7:284-94.

Examples

data(iotf)
## calculate z-scores by sex corresponding to IOTF cutoffs for thinness,
## overweight and obesity
co <- data.frame(cutoff = c(16, 17, 18.5, 25, 30),
  grade = c('thinness 3', 'thinness 2', 'thinness 1',
    'overweight', 'obesity'))
sexes <- c('boys', 'girls')
with(co,
  cbind(co, lapply(setNames(sexes, sexes), function(x)
    LMS2z(x = 18, y = cutoff, sex = x,
          measure = 'bmi', ref = 'iotf'))))