In this paper, some size-biased probability distributions and their generalization have been introduced. These distributions provide a unifying approach for the problems where the observations fall in the non-experimental, non-replicated, and nonrandom categories. These distributions take into account the method of ascertainment, by adjusting the probabilities of actual occurrence of events to arrive at a specification of the probabilities of those events as observed and recorded. Failure to make such adjustments can lead to incorrect conclusions. This paper surveys some of the possible uses of size biased distribution theory to some real life data.