To correct for the potential extrapolation error for ages beyond 70 , the adjustment factor is selected as the ratio of a 70 year old individual 's WTP to a 40 year old individual 's WTP , which is 0.63 , based on the Jones-Lee ( 1989 ) results and 0.92 based on the Jones-Lee ( 1993 ) results .
There might be error for old people .