Example of a STD matrix. An example of a pooling design for 20 compounds, expecting at most 2 active compounds and 0 errors in testing, requiring a 15 × 20 binary matrix, created using STD(n = 20; q = 5; k = 3). A black square represents the presence of a compound j (column index) in test i (row index). The red dashed line represents the separation of the STD design into its 3 layers (k), each of size 5 × 20 (q × n). Each compound is present only once in each layer of the design. Each compound is present at most once (Γ = 1) with every other compound.