This is a technique to economically identify rare subjects within large, poorly-mapped search spaces.
A. Aggregate Pyramiding is a variant of snowballing used to search the best solution for problem in diverse areas including product development, social and scientific problem. Pyramiding is a search process based upon the idea that people having a strong interest in a given attribute or quality, for example a particular type of expertise, will tend to know of people who know more about and/or have more of that attribute than they themselves do (von Hippel et al 1999). For example, if an individual is an expert heart surgeon, pyramiding assumes that that individual will know of others who are still more expert in that field. Similarly, if a person is an avid collector of jazz CDs, pyramiding assumes that person is likely to be able to identify people with still larger collections of jazz CDs. When the best solution is identified using this process the screening costs are minimal compared to other competitive techniques.
[Source - Internet]