Total garden yield is but a crude metric. The chart of collards yield, for example, shows that we are producing a lot more collards this year than before; what it does not show is the fact that we planted 1.5 beds of the stuff this year—probably three times as much as we did last year. We can't normalize the yield to bed area, in other words. We may need to resign ourselves to qualitative comparisons until we exercise more rigor in our data collection.
My intent was not to be wonky about collard yield, but to reassure that the fertility of our garden is not decreasing. We seem to be doing fine.
Graphics reveal data. Indeed graphics can be more precise and revealing than conventional statistical computations.—Edward R. Tufte, The Visual Display of Quantitative Information