I can not explain why "an" is used in the phrase "an estimated 2 million people are".
In addition, I can find many examples in which such phrases are treated as plural although the noun phrase takes "an". When the noun 'people' is a collective noun, it may be possible to say/write "an estimated 2 million people is". But I am not sure about this.
Can anyone explain the grammar?
Best Answer
I would explain it with "an estimated number of two million people". The following verb may be singular or plural as in
1 An estimated number of people was killed in the war.
Here the verb sg refers grammatically to "number" (sg).
2 An estimated number of two million people were killed in the war.
Here the verb pl refers logically to "two million people" (pl).
As a non-native speaker I can't decide which possibility is preferred or more frequent. I would tend to use the verb pl. In the same way as I say "There were a lot of people there". The verb pl refers to the logical idea of "many people" and not to the grammatical head "lot" of the noun group "a lot of people".