Is it correct to combine both present perfect and simple past together as in the sentence below?
This method has saved the lives of many patients as the true diagnosis was missed or unusual.
Is it correct to combine both present perfect and simple past together as in the sentence below?
This method has saved the lives of many patients as the true diagnosis was missed or unusual.
The first phrase indicates a repeat occurrence. The second phrase is merely an explanation of the reason why.
Since it (the wrong diagnosis) would have already occurred (which led to the "method"), this construction is OK.
However I think this would read more naturally with "because" instead of *as" since it is an explanation:
This method has saved the lives of many patients because the true diagnosis was missed or unusual.