Published online by Cambridge University Press: 20 November 2018
An incomplete pairwise balanced design is equivalent to a pairwise balanced design with a distinguished block, viewed as a ‘hole’. If there are v points, a hole of size   $w$ , and all (other) block sizes equal
 $w$ , and all (other) block sizes equal   $k$ , this is denoted
 $k$ , this is denoted   $\text{IPBD}\left( \left( v;w \right),\,k \right)$ . In addition to congruence restrictions on
 $\text{IPBD}\left( \left( v;w \right),\,k \right)$ . In addition to congruence restrictions on   $v$  and
 $v$  and   $w$ , there is also a necessary inequality:
 $w$ , there is also a necessary inequality:   $v\,>\,\left( k\,-\,1 \right)w$ . This article establishes two main existence results for
 $v\,>\,\left( k\,-\,1 \right)w$ . This article establishes two main existence results for   $\text{IPBD}\left( \left( v;w \right),\,k \right)$ : one in which
 $\text{IPBD}\left( \left( v;w \right),\,k \right)$ : one in which   $w$  is fixed and
 $w$  is fixed and   $v$  is large, and the other in the case
 $v$  is large, and the other in the case   $v>\,\left( k-1+\varepsilon\right)w$  when
 $v>\,\left( k-1+\varepsilon\right)w$  when   $w$  is large (depending on
 $w$  is large (depending on   $\varepsilon$ ). Several possible generalizations of the problemare also discussed.
 $\varepsilon$ ). Several possible generalizations of the problemare also discussed.