

More on value functions 
The emphasis on changes as the carriers of value does not mean that the value of a particular change is independent of the initial position. Value functions are likely to become more linear with increases in assets. A change from $100 to $200 is likely to have a much higher value than a change from $1100 to $1200. The value function is then concave above the reference point (v"(x) < 0 for x > 0), and convex below it (v"(x) > 0 for x < 0). Meaning, it is concave for gains and convex for losses. 
More on the weighting function 
The weighting function π, which relates decision weights to stated probabilities, is an increasing function of p, with π(0) = 0 and π(1) = 1. However, people tend to overweight very small probabilities, like 0.001, so that π(p) > p for very small p. 

Page source: http://www.econport.org/econport/request?page=man_ru_advanced_prospect_valweight
