So far we have talked about independent variables primarily in everyday language. We all have a conceptual notion of what we mean by “brightness” or “rate of meaning,” for example. However, because one criterion of science is replicability, it is not enough to have only conceptual definitions. Earlier we talked about color as an IV and blue and yellow as treatment levels. For scientific purposes, we would have to be much more precise in our designation of these colors. There are many shades and hues of blue and yellow (one source----Judd and Kelly, 1965----identified 7500 different colors). In our experiment we would have to specify which blue we are using by giving a standardized definition. Psychologists use the Munsell color chart, developed by Albert Henry Munsell, that describes colors by hue, saturation, and lightness.