Some 1200 fewer people were admitted to hospital with heart attacks than even the prevailing downward trend had suggested was likely.

句子漏掉了 the，限定可数名词 trend。some 修饰数字，等于about。

该句有几个问题需要讨论：

1. than 是  was likely 的主语，意味着它是单数。其对应项不能是 people。再说，likely 不能描述 people。

2. even the prevailing downward trend had suggested 为“嵌入式”，类似 I think，than was likely 为 suggested 的宾语从句。

3. 去掉这个嵌入式 even the prevailing downward trend had suggested，简化句子：

Some 1200 fewer people were admitted to hospital with heart attacks than was likely.

简化后，句子结构不错。问题是： was 的主语是单数，不是 people，它何所指？这里，was likely 的主语只能是“情况”。

Some 1200 fewer people were admitted to hospital with heart attacks than even the prevailing downward trend had suggested was likely.

句子意思：因心脏病发作入院的人数，比盛行的下降趋势所显示的可能情况要少约1200人。

对比例句：

More people hope to live in the countryside than used to (do).

than 是比较代词，它既表示比较意义，又有指代 many people 的作用，暗示在从句中作主语。

More friends will come to his birthday party than did last year.

在 than did last year 中，did 的主语由than 兼任，than 暗示 many friends， did = came to his birthday。

（以上例句，than 暗指“人”）

He never says more than is necessary.

他从不多说没有必要的话。（他从不说废话）

He often eats more than is good for his health.

他通常吃的饭量多于对身体有益的量。

（以上例句，than 暗指“说的话；吃的饭”much，故从句用单数）