I was writing a report of my economic presentation. I had to mention that I chose three states for my studies in the introduction of the report. Since I can't use the active voice to mention this, which passive voice should I chose, passive of simple present or passive of present perfect? i.e 'are chosen' or 'have been chosen'?
Since I can't use the active voice to mention this
Well, "I chose" or "we chose" is perfectly good English. I do know that some college style-guides have a bizarre rule against this. Just remember that it's a bizarre rule of some college style-guides, rather than anything to worry about in the real world.
Aside from that, you should use whichever fits the rest of the description. The simple past "…were chosen…" seems to be the most obvious, but there are certainly reasonable sentences one could write with the other two tenses too.
"…are chosen…" would be referring the the general procedure, while "…have been chosen…" would refer to the specific case.
In conducting this sort of study, the states are chosen on the basis of…
In conducing this study, the states have been chosen on the basis of…
If the goal of such constructions is to avoid first-person subjects ("I chose these three states because..."), then an alternative to the passive voice (which can be irritating in continuous use) is to reify the choosing into a noun phrase ("The choice of three states to study rests on these considerations...").
According to an earlier post here (sorry I don't have time to find it) the difference between "are chosen" and "have been chosen" is that, the latter delivers the meaning you did it. The "are chosen" means rather than it is chosen, but the person who did it's not defined.