bone.RdFrom the web source: "Relative spinal bone mineral density measurements on 261 North American adolescents. 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."
The data are a repackaging and extension of the data of the same name from the now archived (in 2020) of the 2015 `ElemStatLearn` package of Kjetil B. Halvorsen.
The principal changes here is the renaming of the variables gender and spnbmd AND in
the addition of a new variable ethnic derived from the bone_ext data set.
The variables gender and spnbmd were renamed to sex and rspnbmd,
respectively, to better agree with names in the larger and more complete data set bone_ext
taken from the same study and source webpage. The variable ethnic was extracted from
bone_ext by matching `idnum` in the two datasets.
A data frame with 485 rows and 5 variables
Identifies the subject, and hence the repeat measurements
Age of subject averaged over the two times measurements of
spnbmd were taken to determine the relative change rspnbmd.
Sex of the subject. A factor with levels "female" and "male".
Relative spinal bone mineral density measurement.
Each value is the (unitless) difference in spnbmd` taken on two
consecutive visits, divided by the average of the two measurements.
The "ethnicity/race" of the subject. A factor with levels "Asian", "Black", "Hispanic", and "White".
The row order of the values follow their order of appearence in the source webpage.
Trevor Hastie's "Elements of Statistical Learning" page at Stanford.
The purpose of the study was to examine ethnic and sex differences in bone mineral acquisition over time for young (aged 9-25 years) healthy Asian, black, Hispanic, and white males and females. The study recorded areal bone mineral density (BMD) in grams per square centimetre in the lumbar spine.
These data are a subset of 261 subjects taken from a convenience sample of 423 healthy young people of various "ethnicities."
The source website does not describe how this subset was chosen.
Rather than the spnbmd measurement at each visit of a subject (as with `bone_ext`),
the response rspnbmd denotes the relative change in spnbmd between visits and is
calculated as the difference between the later and early visit values of spnbmd divided
by the average of these two values. The `age` variable is similarily taken to be
the average of the subject's ages at the two visits.
On the subjects (Bachrach et al, 1999):
"A convenience sample of healthy youth was recruited from the community through advertisements and personal contact (21, 22). Individuals with a history of medical conditions or use of medications affecting bone mineral were excluded. Subjects were encouraged to return annually for a total of four visits or until they had reached age 26 yr. Recruitment occurred between May 1992 and February 1996; data collection ended in February 1997. The cohort at entry included 103 non-Hispanic whites, 103 Hispanics, 103 Asians, and 114 non-Hispanic blacks, aged 8.8 –25.9 yr; 230 females and 193 males were enrolled as previously reported (22). For simplicity, ethnicity and race will be used as interchangeable terms, and the groups will be referred to as white, Hispanic, Asian, and black. A total of 280 subjects completed 2 visits; 189 were studied 3 times, and 113 were evaluated 4 times. Subjects who completed fewer than 4 visits included those who refused, relocated, or reached age 26 yr during the study period; in addition, subjects who were recruited late in the study did not complete all visits because funding had terminated.
So-called "ethnicity" can be found in the data set `bone_ext`.
See references, particularly Bachrach et al (1999), for more details.
Laura K. Bachrach, Trevor Hastie, May-Choo Wang, Balasubramanian Narasimhan, and Robert Marcus (1999) "Bone Mineral Acquisition in Healthy Asian, Hispanic, Black and Caucasian Youth. A Longitudinal Study", J Clin Endocrinol Metab, 84, 4702-12.
Trevor Hastie, Robert Tibshirani, and Jerome Friedman (2009) "The Elements of Statistical Learning", 2nd Edition, Springer New York <doi:10.1007/978-0-387-84858-7>
R.W. Oldford