Learn Dutch: Begrijpt u het door de onderzoeker berekende percentage? - Do you understand the percentage calculated by the researcher?

In Dutch, you can take a simple noun phrase like het berekende percentage (the calculated percentage) and stretch it out to include more details. All the extra information—in this case, door de onderzoeker (by the researcher)—is placed right between the article (het) and the participle (berekende). English usually puts this modifying information after the noun.

Why does the past participle berekend get an -e at the end here?

When a past participle is used as an adjective directly in front of a noun, it follows standard adjective inflection rules. Percentage is a het word. Because it is preceded by the definite article het, the modifying participle (berekend) must get an -e at the end, becoming berekende.

Could I phrase this differently and put the extra information after the noun, like in English?

You cannot simply place the bare participle phrase after the noun like in English. To avoid the accordion structure, you must build a full relative clause instead: Begrijpt u het percentage dat door de onderzoeker is berekend? (Do you understand the percentage that was calculated by the researcher?). Both versions are correct, though the accordion style is highly typical for formal writing and news.

Why is door used here to mean "by"? Doesn't it usually mean "through"?