As an exception, for the utility (or else quality of life) parameters (with and without dementia), we used a relative standard error of 5% to restrict the cases where people attach higher utility to having de- mentia than not to having it, which is hardly realistic. Vita- mins were assumed not to have negative impact on health and therefore, incremental QALYs can theoretically never become negative in our analysis. However, we allowed in- cremental QALYs to take negative values to incorporate extreme, close to unrealistic, cases in which treated patients would value the disutility of taking vitamins every day dur- ing the gained dementia-free years higher than having de- mentia in the same period. Moreover, the model assumed that people would receive B-vitamin treatment until demen- tia onset or death.