About parenthetical expressions, is the sentence grammartically correct?

Question

This novel method has significantly improved the research period from one year in previous attempts, due to a lack of observatory data, to the longest year with reliable documentary data, 100 years in this study.

Not sure if the meaning is clear, I would like to emphasize the improvement of methods. In the previous studies, the research period is only one year. Using the new method, the research period can be extended to many years back in time as long as reliable data are available.

Answer 1

At the least you should not use "year" in the way you have; "longest year" is confusing as it suggests that the length of a year changes substantially. A possible alternative would be:

"to the longest period with reliable documentary data"

Some re-structuring of your sentence might make your meaning more explicit, though. For example:

"Previous analyses have been limited to a research period of one year, by a lack of observatory data; this novel method allows the research period to be extended over a much longer timescale (100 years in the present study) determined by the earliest date at which reliable data is available."

I'd comment though, that this wording might be further improved/corrected, but I am not clear from your question of a couple of points of necessary information:

1. What is the difference between the "observatory data" which is missing for periods >1 year, and the "reliable data" which is available from 100 years back?
2. Does the "reliable data" just have to be available from some time in the past, or does your method need a continuous run of data for the 100 year period?

I am assuming this is a concluding summary in a technical paper - and of course it is important to be specific and accurate in such a situation.

Answer 2

The main problem with parenthetical expressions is that, if they are confusing or too long, they only distract from the point you are trying to make. You want the reader to return to the main point and remember how the sentence started. Sentences with parenthesis should also make completely grammatical sense if you removed the parenthetical expression.

If I understand correctly what you are trying to say, I feel that a clearer, more succinct way to express it would be:

This novel method has significantly improved research over previous attempts, where only one year of data was available, by giving us 100 years of reliable documentary data to study.

This briefer parenthetical expression contains only what is relevant about the previous attempts as a comparison to the improvements with the new method.