# A choice between singular and plural

A significant decrease in the score was observed 1 and 2 months after the intervention.
Significant decreases in the scores were observed 1 and 2 months after the intervention.

Which of the above is grammatically correct? Would the latter correct because the decreases observed from different time points are apparently different kinds of things?
+ Should I put 'at' and make the sentence '~~ observed at 1 and 2 months ~~'? Or is it alright without 'at'?

You really have a choice in this context. There is no correct answer.

However, if the decrease was much the same after each month, and there was a single score, it might incline you to use the singular.

If the decreases varied widely, if there was a series of decreases rather than just one, and if there was more than one score, you should use the plural.

It's fine without at. You could insert it if you chose.

Ronald Sole has given an excellent answer to the specific question asked, but both sentences suffer from the same potential ambiguity.

Old score = 100 Score at end of month 1 = 80 Score at end of month 2 = 80

There was a material decrease (20%) relative to the same base in both months. Either sentence reflects that.

Old score = 100 Score at end of month 1 = 80 Score at end of month 2 = 64

There was a material decrease (20%) relative to different bases in each month. Either sentence reflects that.

But those are two different situations entirely.

For the first situation

There was a material decrease in the scores at the end of the first month, but no further material changes at the end of the second month.

For the second situation

There was a material decrease in the scores at the end of the first month, and a further material decrease in the scores at the end of the second month.

Now this answer will be pettifogging if this text supplements a table or a graph. In that context, either of your sentences will be interpreted correctly. If, however, you are trying to provide a purely qualitative summary of something that is inherently quantitative, either sentence is subject to misinterpretation.