The random allocation method is based on blocking. Four blocks are used. The list of 24 blocks is written and randomly a number is selected and the sampling is continued based on it
ABCD, ABDC, ACBD, ACDB, ADBC, ADCB, BACD, BADC, BCAD, BCDA, BDAC, BDCA, CABD, CADB, CBAD, CBDA, CDAB, CDBA, DABC, DACB, DBCA, DBAC, DCAB, DCBA