6. GNP is an imperfect measure of current production. It excludes household production. It fails to account for the negative side effects of current production such as air and water pollution, adverse impacts on health, depletion of natural resources, and other factors that do not flow through markets. It imperfectly adjusts for quality changes. GNP comparisons are less meaningful when the typical bundle of available goods and services differs widely between two time periods (or between two nations) .