Everyone knows the computer business is big, but nobody seems to know exactly how big or who has what piece of it. That is how the folks at the Comtec Market Research Program sized up the situation, anyway, when they set out to assemble a study of representative computer installations throughout the country.

"Comtec exists in recognition of the fact that there had been only bad estimates of market share and size done for these industries in the past," explains C. Oakley Mertz, vice-president of Gartner Group Inc. "I called most of the past studies 'supply-side consensus.' Information came from informal interviews with vendors, even though the researchers knew the vendors would exaggerate numbers to make themselves look good. We decided it would be more accurate to create a sample of users."

Gartner Group, a computer market research firm in Stamford, Conn., and Burke Marketing Services Inc. of Cincinnati, and Infratest International GMBH of Munich, West Germany, performed the research. Comtec surveyed a sample of some 8,000 companies last summer and began publishing the data early this year, in a series of 15 volumes that range in price from about $20,000 to $75,000.