<qa>  What is the goal of the study design?CLASP is a research study to investigate the safety and effectiveness of simvastatin a cholesterol lowering drug or statin to slow the progression of AD. The clinical trial will include the treatment of patients with mild to moderate AD, and the objective is to evaluate the safety and efficacy of simvastatin to slow the progression of AD, as measured by the cognitive portion of the AD Assessment Scale. Measures of clinical global change ADCS-CGIC, mental status, functional ability, behavioral disturbances, quality of life and economic indicators will be made also. The study design is randomized, double-blind, placebo-controlled, parallel group design with equal randomization to drug and placebo. Randomization will be stratified and blocked to ensure balanced assignment within site. Sample size will include 400 participants enrolled from approximately 40 sites with a goal of 10 to 15 volunteers enrolled at each site. Study medication will be as follows: 20 mg of simvastatin or matching placebo to be given for 6 weeks, followed by 40 mg of simvastatin or matching placebo for the remainder of the 18-month study period. Participants will be instructed to take the medication once a day in the evening. Safety parameters to be checked will include adverse events, symptom checklists, vital signs, physical and neurological examinations, and laboratory tests. 