Preliminary Or Exploratory Uses

While not always confined to being exploratory methods, PC A, CA, and FA are often used for that purpose. Of the three, PC A is probably the one most used to examine data to learn how the data should be subsequently examined to secure the greatest amount of value from them. Basically, PCA is a procedure for examining the variance of data to learn which variables go together and which others belong to a different group. The procedure thus performs two functions. It establishes whether there is correlation among some of the variables (sensory scores and instrumental measurements); then it attempts to reduce the dimensionality of the data, ie, groups together in a component those things that are correlated with each other.

Variance, or dispersion, should perhaps be defined. It is a measure of the degree to which measurement values should in theory be the same rather than differ slightly, as they usually do. The variation represents error, not in the sense that the measurement is wrong but in the sense that measurements made on the same sample are usually not identical. Among causes of error, generally minor, are periodic inconsistencies in the performance of the instrument. Slightly more common are variations in results caused by the operator of the instrument not being entirely consistent in his or her handling of the instrument or samples. The most prevalent cause of variance is the inherent differences that characterize all biological materials—and a very high proportion of specimens examined for sensory qualities are biological in nature: nearly all our foods and beverages are. Other materials such a perfumes may be compounded from differences substances, but many of the most desirable ingredients are extracted from natural substances. Such things as air or water pollutants, although not necessarily biologically derived, likewise vary according to the way the wind blows and how an industrial plant is being operated. Error should not, therefore, be looked on as "wrongness" but rather "lightness" in the sense that all things exhibit some variation in their properties and performance, and the error term is merely reflecting that.

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