Robustness of BIB and extended BIB designs against the unavailability of any number of observations in a block

Robustness of block designs is investigated, when any observations in a block are lost, in terms of efficiency of the residual design. The designs are balanced incomplete block (BIB) and extended BIB designs. The investigation shows that the covered designs are fairly robust against the unavailability of any number of observations in a block. Furthermore, the robustness of any Youden design and Latin square design against the loss of a whole column is shown.