1、that 是指代前面作主语的 result.这样用的目的是为避免前后两个 the result 的重复而使句子更加简洁.其实如果啰嗦起来,就是 The resultis similar to (that result) (which is) reported by Levy in 1980.
that/those 常用于指代上文提到过的同类特指事物或类型.另如：
Indoor pollution falls into two categories, that which wecan see or smell, and pollution which is invisible and produces no odour. 室内污染分为两种：一种是我们能看得见或闻得着的,另一种是无色无味的.【that 指代上文提到过的twocategories 中的一种】
The relics found were those of an earlier time. 所发现的遗迹是较早的年代（同类遗迹）.【those 指代与上文同类的复数名词the relics】
2、如果省略作主语的关系代词 which/that,就会使定语从句中的谓语动词失去“主心骨”,从而成为不完整的句子,就不能称其为从句.如果想借用先行词作逻辑主语,用分词短语作定语,不仅要省略关系代词,还需要把原谓语动词变成相应的分词,即主动语态变成现在分词,被动语态连同助动词be省略后变成过去分词.如：
That is the parcel (which came) this morning. 那就是早上送来的包裹.
可以省略为That is the parcel (coming)this morning.
The movie (which was shown) later was better. 后来上映的电影较好看.
可以省略为The movie (shown) later wasbetter.
是否可以这样理
因为后半句中that是指代前面的result,不是定语从句中作主语的关系代词（which/that）,所以后半句不是定语从句的结构。又因为后半句是被动关系，所以要用过去分词表示被动作后置定语（省略be）？
定语从句中关系代词指代物作主语时，关系代词which/that 不能够省略，只有指代物作宾语时才能省略关系代词，对吗？