Warning: contains spoilers for Harley Quinn #15 and Shadow War Zone #1!
In DC Comics, many know of Harley Quinn's professional title as Dr. Harleen Quinzel. However, Harley's original job description has fluctuated in various adaptations, generally flip-flopping between psychiatrist and psychologist as needed for the plot. However, it doesn't make sense to use these terms synonymously, as they're both very different professions. Finally, DC has settled the debate.
Many aren't familiar with the differences between a psychologist and psychiatrist, those roles being used interchangeably in various forms of media, including comic books. A psychologist is someone who requires a PhD qualification; they study human behavior and treat their patients through therapy. Psychiatry, on the other hand, is a medical field, which requires an MD. They focus more on the science of the brain, studying its biological and chemical imbalances, and prescribing medication to their patients. Even in her comic-book origin following Harley's rise in popularity in Batman: The Animated Series, creators Paul Dini and Bruce Timm couldn't decide what kind of doctor she was. In the span of five pages, readers learned that Harley somehow had a PhD in Psychology and had attended med school before starting work at Arkham Asylum.
So, which is it? In Harley Quinn #15, written by Stephanie Phillips and drawn by Riley Rossmo, readers get their answer. "In psychology we have this term called 'masking'..." Harley says, observing the violence wreaked by Verdict, a masked villain with an agenda against a certain Mistress of Mayhem. She confirms her qualifications while also reflecting on the Joker's cruel treatment towards her. "Mister J used to tell me I wasn't smart enough to help with his plans... He said my PhD was just a piece of paper." DC confirms this version of Harley's backstory in Shadow War Zone #1's 'Ninjas at the Arcade' - from Stephanie Phillips and Ann Maulina - as Batwing states she possesses, "a doctorate in psychology with hundreds of clinical hours logged with Gotham's most criminally insane" and "a dissertation on personality disorders."
The specific mention of Harley having a "doctorate in psychology" and the way in which she analyzes the concept of masking as a social concept - something a psychologist would discuss, not a psychiatrist - settles her former profession, especially since both stories are set in DC's main canon. As a bonus, Shadow War Zone also mentions clinical hours at Arkham, explaining why she originally began working at the asylum where she'd eventually meet Joker. Harley has always demonstrated a shrewd understanding of emotions and behavior, with one of her greatest strengths being her ability to read people, so the choice to codify her as a psychology is a smart one.
After years of back-and-forth depending on the creative team, it's specifically confirmed that Harley Quinn is a qualified psychologist, PhD and all. Despite being so regularly labelled as a psychiatrist, her portrayal as a character doesn't suit that role. Harley Quinn's characterisation in the comics and her empathetic demeanor make psychologist seem like a far more viable role.
Harley Quinn #15 and Shadow War Zone #1 are available now from DC Comics.