Define Probability concept of requirements vs risk of deficient and excess intake?

Figure best illustrates the concept of a requirement for an essential nutrient. The relationship between the level of intakes and the probability that the intake is deficient or excess, is portrayed in this Figure. As you may have noticed, the estimated average requirement (EAR) is the intake at which the risk of the inadequacy is 0.5 (50 percent) to an individual.

The intake at which the risk of inadequacy is judged to be essentially zero is taken as the requirement for that nutrient. As the intake rises above this level, a point is reached when risk of excess exceeds zero. The range between the intake level at which risk of deficiency is zero and the point at which the risk of excess rises above zero is taken as the 'safe range of intakes'. This concept is utilized in deriving the recommended dietary intakes (RDAs) and the upper intake level (UL) for all the nutrients except energy.