trtools: Miscellaneous Tools for Teaching Statistics

#' Impact of pesticides on skylark reproductivity. 
#'
#' The data are from a cross-over design in which four fields were either sprayed or not on each of four consecutive years. For each field on each year, the number of skylark fledglings produced was recorded. 
#'
#' @format A data frame with 16 observations and four variables:
#' \describe{
#'    \item{year:}{year on which the observation was made}
#'    \item{field:}{identifier for the field}
#'    \item{spray:}{was the field sprayed that year?}
#'    \item{count:}{number of skylark fledglings}
#' }
#' 
#' @details These data are from a study discussed by Odderskær et al. (1997) and were featured in Tjur's (1998) article on overdispersion in generalized linear models. 
#'
#' @source Odderskær, P., Prang, A., Eknegaard, N., & Andersen, P. N. (1997). Skylark reproduction in pesticide treated fields (Comparative studies of Alauda arvensis breeding performance in sprayed and unsprayed barley fields). Bekæmpelsesmiddelforskning fra Miljøstyrelsennr. 32, National Environmental Research Institute, Ministry of the Environmnent and Energy, Denmark: Danish Environmental Protection Agency. 
#' 
#' Tjur, T. (1998). Nonlinear regression, quasi likelihood, and overdispersion in generalized linear models. \emph{American Statistician}, \emph{52}, 222-227.
"skylark"