The people of America are demanding a change; _______, studies conducted by sociologists and psychologists are being used to affect a change. [emphasis added]
Effect! Which means "to bring about".
The proper use of "affect" and "effect" can be mildly confusing, but most English majors and teachers should be able to make the distinction. What's troubling is that the editor of this text -- one that is designed to teach students how to write properly -- could not.
In a nutshell, "affect" is usually a verb meaning to influence something else (Ex.: The play affected me emotionally.) while "effect" is usually a noun that describes a result (Ex.: Watching the play after eating nachos had the effect of making me sick.).
Usually is the key word.
"Affect" can be a noun meaning emotion or feeling, but this use is not very common. Also, "effect" can be a verb meaning to bring about, to cause to happen. And this is the meaning that best fits the question above.
To write well, make sure you always have the proper word choice. The dictionary is your friend; use it. And always, always double check potentially confusing word choices. If you think you have it right, check it again. Then check one more time. We all make mistakes, but a little diligence can go a long way toward clarity.