Figure 1 Primary objectives, theoretical designs, and optimal duration of clinical trials in MCI. Solid lines indicate minimum trial duration and dashed lines optimal trial duration. Probable disease modifying effect requires a randomised start or randomised withdrawal design,⁵⁴,⁵⁶ where after delayed start or withdrawal of active treatment the placebo group does not converge with the treatment group. The last design is a theoretical and has not been applied in either AD or MCI trials.