ABSTRACT
The interpretation of measurements often involves checking them against critical levels of the variables to which they refer. These are levels below which it is generally agreed there is evidence of an unacceptable degree of immediate or impending distress. A normal characteristic of an indicator is that it is used to show a number of different aspects of the performance of a system. Among the more important variables that reflect on the operation of food systems are data on food supplies collected at national level, which are commonly expressed as per capita protein or energy availability. Amartya Sen has commented that the poor of India 'may not be accustomed to receiving much help', but they are 'beginning to get used to being counted'. In screening a particular population, for example, people might have resources to treat all those on the 10th centile and below.
