The researcher structures the study by addressing three topics which include the research question, the researcher’s perspective and also the sample selection.

On the above sentence, do I need to put a colon after include, or is the sentence fine the way it is?

The sentence is fine the way it's written.

Check this site.

http://grammar.ccc.commnet.edu/grammar/marks/colon.htm

In the given sentence, a colon is not required after the word "include." The sentence is structured correctly without it. Let's break down the sentence to understand why:

"The researcher structures the study by addressing three topics which include the research question, the researcher’s perspective, and also the sample selection."

This sentence is a complex sentence that contains a main clause ("The researcher structures the study") and a dependent clause ("by addressing three topics"). Within the dependent clause, we have a phrase that lists the three topics: "which include the research question, the researcher’s perspective, and also the sample selection."

Here, the word "include" serves as a verb to show that the three topics are part of the dependent clause. Since the list is not a complete sentence on its own, a colon is not necessary. The sentence is grammatically correct as it is.