More generally, the inflation adjusted cost of energy and resources have continually declined when measured over periods of greater than ten years. Contrary to the theory that increased population causes a decrease in material wealth, the twentieth century saw a dramatic and consistent increase in population along with a dramatic and consistent increase in material wealth. A more balanced view of energy and resources can be found in The True State of the Planet, a compendium of papers written by ten environmental scientists who publish in peer reviewed journals [Bailey1995]. A number of the energy books we reference below suffer from the same basic flaw, however, once you get past the preface and first chapter of these various books, they tend to be pretty reasonable.