the R-package agricolae and is specified in the following table: The investigator chooses the parameters , and for the block design which are then inserted into the R-function. Subsequently, the remaining parameters and are determined automatically. Using the basic relations we calculate that we need blocks, that is, 3 test people in order to obtain a balanced incomplete block design. Labeling the blocks and , to avoid confusion, we have the block design, }, } and }. A corresponding incidence matrix is specified in the following table: Each treatment occurs in 2 blocks, so . Just one block () contains the treatments 1 and 2 simultaneously and the same applies to the pairs of treatments (1,3) and (2,3). Therefore, . It is impossible to use a complete design (all treatments in each block) in this example because there are 3 sunscreens to test, but only 2 hands on each person. See also Incidence geometry Steiner system Notes References . 2nd ed. (1999) . External links DesignTheory.Org: Databases of combinatorial, statistical, and experimental block designs. Software and other resources hosted by the School of Mathematical Sciences at Queen Mary College, University of London. Design Theory Resources: Peter Cameron's page of web based design theory resources. Combinatorics Combinatorial design Families of sets Design of experiments