Her belief that caffeine is good for health is totally off-base.

off-base 是一个复合形容词，由介词 off（偏离）和名词 base（基础、基准）组成，字面意思是"偏离基准的"。在口语中引申为"错误的、不准确的"，用来形容观点或判断与事实不符。