In The Great Pretender (Grand Central, Nov.), journalist Cahalan finds significant issues in psychologist David Rosenhan’s influential 1973 study “On Being Sane in Insane Places.”

What did you learn writing this book?

When I started, I wanted to uncover the real story in a very positive way—to find the pseudopatients and explore their experiences and motivations. And of course, my own experience [of being psychiatrically misdiagnosed]really aligned with theirs. I felt like a kindred spirit. Obviously, as the investigation unfolded and I learned more about the history of psychiatry, the story changed. Things I felt I knew, I started to doubt.

What made you realize you were on to something?

The medical records [from the hospital to which Rosenhan was admitted], which were a real indication that this was not the full story. I came into this study as a true believer. So, when I found those records, I suddenly realized that this was a different story than the one I intended to write. Secondly, it was finding another pseudopatient, and his story not fitting into Rosenhan’s narrative.

What was the greatest challenge you faced in conducting your research?

Not having David here to talk to and interview. I felt a responsibility in grappling with what am I doing to this man’s legacy while being fair and honest. My major source was not there to critique or deny or support my theories. I did not have that center. I was orbiting around somebody who is dead.

You write that “belief is what psychiatry has lost—and what it needs to survive.” How can it be restored?

Being honest about the limitations, because medicine in general relies on belief, and belief gets shattered when we pretend to have more knowledge than we do. Rosenhan’s study contributed to a push for the field to defend itself, and I think that was a reaction out of fear and embarrassment. Ultimately, the way we move forward is knowing what we do not know, or at least acknowledging that we do not know so much.

You’ve already seen your first book adapted for film. How would you envision this book translating to the big screen?

I think the book itself would be hard to adapt, because it is a lot of history and academic research. But, I do have an idea. There could be a psychiatric hospital, where there’s a rumor that someone is faking it. Then, the viewer is complicit in terms of judging people and diagnosing. This would pose the question that David Rosenhan had—what is sanity and what is insanity?—and answer it: we are all in a continuum, and of course there is extreme dysfunction, but there are also gradients.