If these data are statistically valid, it will help us to understand the problem under investigation. That's right, because "problem" refers to the "problem" we are investigating. As can be seen from the Chinese meaning, the question of "one" is investigated, and the plural form is not needed, and the attached words are wrong (because the Chinese meaning does not reflect the words that should be plural, such as these).

Expand:? When do you add S to fruit?

When the fruit refers to "fruit", it is collectivized without adding S.

When fruits refer to classified fruits, you can add S.

Like what?

I want to buy some fruit.

I want to buy some fruit. (The fruit here refers to the fruit, you can't add S, use the prototype. )

I like bananas, apples, pears and other fruits.

I like bananas, apples, pears and other fruits. (Classification of fruits here, plus S, plural form)