The concept of a broader measure of economic welfare than income per head. This could include in addition to ordinary measures of income items such as the following: the cost of effort; the value of household production, including services such as childcare and looking after the sick and elderly; any depletion of the stock of natural resources; and the value of changes in the natural environment. While such a measure of overall welfare would be of great interest, the observation and valuation of the components is so difficult that any proposed measure would remain highly subjective. See also happiness index.