R/twins.R

In RbyExample: Data for the Book "R by Example"

#' Twins Income and Education Levels Data
#'
#' The data were collected at the 16th Annual Twins Day Festival in
#' Twinsburg, Ohio, in August 1991. 495 adult twins were interviewed. The
#' original study aimed to investigate
#' 'By how much will another year of schooling most likely raise one's income?'
#' Pairs of twins provide a control on confounding factors such as intelligence,
#' family background, etc.
#'
#'
#'
#' @format 183 obs. of  16 variables:
#' \describe{
#' \item{DLHRWAGE}{the difference (twin 1 minus twin 2) in the logarithm of hourly wage, given in dollars.}
#' \item{DEDUC1}{the difference (twin 1 minus twin 2) in self-reported education, given in years.}
#' \item{AGE}{Age in years of twin 1.}
#' \item{AGESQ}{AGE squared.}
#' \item{HRWAGEH}{Hourly wage of twin 2.}
#' \item{WHITEH}{1 if twin 2 is white, 0 otherwise.}
#' \item{MALEH}{1 if twin 2 is male, 0 otherwise.}
#' \item{EDUCH}{Self-reported education (in years) of twin 2.}
#' \item{HRWAGEL}{Hourly wage of twin 1.}
#' \item{WHITEL}{1 if twin 1 is white, 0 otherwise.}
#' \item{MALEL}{1 if twin 1 is male, 0 otherwise.}
#' \item{EDUCL}{Self-reported education (in years) of twin 1.}
#' \item{DEDUC2}{the difference (twin 1 minus twin 2) in cross-reported education.}
#' \item{DTEN}{the difference (twin 1 minus twin 2) in tenure, or number of years at current job.}
#' \item{DMARRIED}{the difference (twin 1 minus twin 2) in marital status, where
#'  1 signifies "married" and 0 signifies "unmarried".}
#' \item{DUNCOV}{the difference (twin 1 minus twin 2) in union coverage, where
#' 1 signifies "covered" and 0 "uncovered".}
#' }
#' @note
#' There are 183 cases; 147 complete cases.
#' Twin 1's cross-reported education is the number of years of schooling completed by twin 1 as reported by twin 2.
#' For data analysis, the logarithm of the hourly wage is typically used instead of hourly wage.
#' @source Guido Imbens, PhD. UCLA, Department of Economics.
#' @references
#' Ashenfelter, Orley and Krueger, Alan.  "Estimates of the Economic Return
#' to Schooling from a New Sample of Twins."  The American Economic Review
#' 84.5 (Dec. 1994) 1157-1173.
"twins"