Trend analysis as a category consists of many, mostly quantitative, techniques. We identify six techniques that have proven to be the more useful overall in business environments. They are precursor developments, trend extrapolation, the Pearl curve, the learning curve, substitution, and multiple substitution.

Forecasting using precursor developments can be done when a lead-lag relationship can be established between two technical areas. This is usually done by observation over a period of years, and establishing causal connections between the technical areas.

Trend extrapolation involves plotting key parameters of technical progress against time. From the results, regular development patterns can be discerned. An initial assumption can be made that the patterns, which are rooted in past developments, can be extended into the future for some period of time. In a large number of technical areas, it has been found that if progress is plotted versus time, the trace is linear on a semilog graph. This would represent a constant percentage rate of change.

The Pearl curve - named for the American demographer Raymond Pearl, who used it in demographic forecasting, is one example from a family of growth models. These techniques are often used to describe technological change patterns that resemble organic growth. The slope of the Pearl curve is a function of both the distance to go to the upper limit for growth and the distance already covered.

The learning curve is a production-driven performance technique. Its basic premise is that as the number of units produced doubles, the labor hours per unit decrease by a constant factor.

Substitution analysis is used to forecast the rate at which one technology will replace another. The traditional approach involves the simplification of the Fisher-Pry model. This model predicts characteristics loosely analogous to those of biological system growth. Many examples now exist for technology substitution.

Multiple substitution represents an increasingly common situation in which either more than one new technology is substituted for an old one or a single new technology is actually replacing more than one old technology.