Flickr/Jane Rahman Depression is the leading cause of disability worldwide, and it can kill. But scientists know surprisingly little about it. Even with awareness programs like World Mental Health Day, which happens every year on October 10, our knowledge of the condition is extremely limited.

We do know, however, that talking seems to help — especially under the guidance of a licensed mental health professional. But therapy is expensive, inconvenient, and often hard to approach. A recent estimate suggests that of the roughly one in five Americans who have a mental illness, close to two-thirds have gone at least a year without treatment.

Several Silicon Valley-style approaches to the problem have emerged: There are apps that replace the traditional psychiatry office with texting, and chat rooms where you can discuss your problems anonymously online.

The newest of these tech-based treatments is Woebot, an artificially intelligent chatbot designed using cognitive-behavioral therapy, or CBT, one of the most heavily researched clinical approaches to treating depression.

Before you dismiss Woebot as a half-baked startup idea, know that it was designed by Alison Darcy, a clinical psychologist at Stanford, who tested a version of the technology on a small sample of real people with depression and anxiety long before launching it.

"The data blew us away," Darcy told Business Insider. "We were like, this is it."

The results of the trial were published Tuesday in the Journal of Medical Internet Research Mental Health.

For the test, Darcy recruited 70 students who said they experienced symptoms of depression and anxiety and split them into two groups. One group spent two weeks chatting with Woebot; the other was directed to a National Institute of Mental Health e-book about depression. Over two weeks, people in the Woebot group reported not only chatting with the bot almost every day, but seeing a significant reduction in their depressive symptoms.

That's a promising result for a type of treatment whose results have so far been tough to quantify — we don't have a lot of research comparing bot-to-human therapy with traditional human-to-human therapy.

Woebot uses CBT to talk to patients, and several studies suggest the approach lends itself to being administered online. A review of studies published recently in the journal World Psychiatry compared people who received CBT online with people who received it in person and found that the online setting was just as effective.

Alison Darcy. Alison Darcy / Woebot Labs One reason for this, according to Darcy, is that CBT focuses on discussing things that are happening in your life now as opposed to things that happened to you as a child. As a result, instead of talking to Woebot about your relationship with your mom, you might chat about a recent conflict at work or an argument you had with a friend.

"A premise of CBT is it's not the things that happen to us — it's how we react to them," Darcy said.

Woebot uses that methodology to point out areas where a person might be engaging in what's called negative self-talk, which can mean they see the environment around them in a distorted way and feel bad about it.

For example, if a friend forgot about your birthday, you might tell Woebot something like, "No one ever remembers me," or "I don't have any real friends." Woebot might respond by saying you're engaging in a type of negative self-talk called all-or-nothing thinking, which is a distortion of reality. In reality, you do have friends, and people do remember you. One of those friends simply forgot your birthday.

"Self-talk is a part of being human," Darcy said. "But the kinds of thoughts that we have actually map onto the kinds of emotions we're feeling."

Darcy is quick to point out that Woebot is not a replacement for traditional therapy, but an addition to the toolkit of approaches to mental health.

"I tend to not think of this as a better way to do therapy. I think of this as an alternative option," Darcy said. "What we haven't done a good job of in the field is give people an array of options. What about the people who aren't ready to talk to another person?"