bone_ext.RdThese are measures on spinal areal bone mineral density. The data are taken from the "large" bone density dataset on the source website (see source).
A data frame with 1003 rows and 5 variables
Identifies the subject, and hence the repeat measurements
The "ethnicity/race" of the subject. A factor with levels "Asian", "Black", "Hispanic", and "White".
The age in years of the subject at the time the measurement spnbmd was taken.
Sex of the subject. A factor with levels "female" and "male".
The spinal areal bone mineral density (BMD) measurement in grams per square centimetre.
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.
The sample was a convenience sample of 423 healthy young people of various "ethnicities."
On the subjects (Bachrach et al, 1999):
"A convenience sample of healthy youth was recruited from the community through advertisements and personal contact. 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."
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