  Experimental crossover designs are widely used in medicine, agriculture, and
other areas of the biological sciences. Due to the characteristics of the
crossover design, each experimental unit has longitudinal observations and the
presence of drag effects on the response variable. There is no package in {R}
that clearly models data from crossover designs. The {CrossCarry} package
presented in this paper allows testing any crossover design as long as the
observed response variable belongs to the exponential family, regardless of
whether or not there is a washout period. It also allows modeling repeated
measurements within each period and extends the correlation structures used in
the generalized estimating equations. The family of correlation structures is
built that takes into account the particularities of the design, that is, the
correlation between and within the periods. It also includes a parametric
component for modeling treatment effects and a non-parametric component for
modeling time effects and carry-over effects. The non-parametric component is
estimated from splines inserted into the generalized estimation equations.
