Bone Mineral Density Data

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Description

Measurements in the bone mineral density of 261 north american adolescents, as function of age. Each value is the difference in spnbmd taken on two consecutive visits, divided by the average. The age is the average age over the two visits.

Usage

1

Format

A data frame with 485 observations on the following 4 variables.

idnum

identifies the child, and hence the repeat measurements

age

average of age at two visits

gender

a factor with levels female male

spnbmd

Relative Spinal bone mineral density measurement

Source

Bachrach LK, Hastie T, Wang M-C, Narasimhan B, Marcus R. Bone Mineral Acquisition in Healthy Asian, Hispanic, Black and Caucasian Youth. A Longitudinal Study. J Clin Endocrinol Metab (1999) 84, 4702-12.

Examples

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summary(bone)
# We ignore the repeat measurements:
# smooth.spline is in standard package stats.
names(bone)
# Plot page 128 in the book:
plot(spnbmd ~ age, data=bone, col = 
     ifelse(gender=="male", "blue", "red2"), 
     xlab="Age", ylab="Relative Change in Spinal BMD")
bone.spline.male <- with(subset(bone,gender=="male"),
                smooth.spline(age, spnbmd,df=12))
bone.spline.female <- with(subset(bone, gender=="female"), 
                smooth.spline(age, spnbmd, df=12))
lines(bone.spline.male, col="blue")
lines(bone.spline.female, col="red2")
legend(20,0.20, legend=c("male", "Female"), col=c("blue", "red2"), 
          lwd=2)