Statistical model
All individuals start in the control condition, and in each time period a number of individuals crosses over the intervention. The number of time periods 
Here, The model can be written in matrix–vector notation. The model for individual 
where
is the vector of length 
is the 
is the vector of length 
is the vector of length 
is the Given an estimate 
with corresponding variance–covariance matrix
The treatment effect estimate The stepped-wedge design is a multi-period design, and it is very likely individuals drop out during the course of the study. The last observation of individual 
The proportion individuals allocated to sequence In practical settings, the lower and upper bounds 0 and 1 for A simple equation for the relation between the allocation 