add uk1990 docu and liveliver

DESCRIPTION

@@ -2,11 +2,11 @@ Package: childsds
 Title: Data and Methods Around Reference Values in Pediatrics
 Version: 0.6.7
 Authors@R: person("Mandy", "Vogel", email = "mandy.vogel@googlemail.com", role = c("aut", "cre"))
-Description: Calculation of standard deviation scores adduced from different
+Description: Calculation of standard deviation scores and percentiles adduced from different
     growth standards (WHO, UK, Germany, Italy, China, etc). Therefore, the calculation of SDS-values
     for different measures like BMI, weight, height, head circumference, different
     ratios, etc. are easy to carry out. Also, references for laboratory values in
-    children are available: serum lipids, iron-related blood parameters. In the
+    children and adults are available, e.g., serum lipids, iron-related blood parameters, IGF, liver enzymes. In the
     new version, there are also functions combining the lms() function from package 'gamlss' with
     resampling methods for using with repeated measurements and family dependencies. A searchable list
     of items can be found here: <https://github.com/mvogel78/childsds/wiki>.

NEWS.md

@@ -1,6 +1,7 @@
 # childsds 0.6.7
 ## Major changes
 * add uk1990 references
+* add liver enzymes references
 ## Minor changes
 # childsds 0.6.6
 ## Major changes

R/data.R

@@ -211,3 +211,19 @@ NULL
 #' @source Olsen, I.E., Groveman, S.A., Lawson, M.L., Clark, R.H., Zemel, B.S., 2010. New intrauterine growth curves based on United States data. Pediatrics 125, e214-224. doi:10.1542/peds.2009-0913
 NULL
 
+
+#' Parameters for serum liver enzymes
+#' @name life_liver.ref
+#' @docType data
+#' @usage life_liver.ref
+#' @source Bussler et al, New pediatric percentiles of liver enzyme serum levels (ALT, AST, GGT): effects of age, sex, BMI and pubertal stage, Hepatology 2017
+NULL
+
+
+#' Parameters from the 1990 UK growth study
+#' @name uk1990.ref
+#' @docType data
+#' @usage uk1990.ref
+#' @source Cole, T.J., Freeman, J.V., Preece, M.A., 1998. British 1990 growth reference centiles for weight, height, body mass index and head circumference fitted by maximum penalized likelihood. Statistics in medicine 17, 407–429.
+#' @source Cole, T.J., Freeman, J.V., Preece, M.A., 1995. Body mass index reference curves for the UK, 1990. Archives of disease in childhood 73, 25–29.
+NULL