Probabilities of voids

We develop a method for computing the probability densities of spherical voids in the distribution of galaxies on a large scale. This method is applied to Poissonian clustering models. We consider CDM biased and non-biased models; the appropriate approximation has been used in each case. We find that, in the latter case, the probability of finding a void like that of Bootes within the CFA catalogue is very small. For the former case, we study the dependence of the probabilities of voids on the biasing factor. For the appropriate value of this variable, the results are in good agreement with the observations. (author)