What Are Double Blind Studies? Why Are They Important?

Not too long ago, when I heard the term double blind study, I had to resist the urge to roll my eyes.

I could hear Seinfeld’s voice in my head:

“Double blind?! What, being blind ONCE wasn’t good enough??”

In reality, though, the world of research wouldn’t be what it is today without double blind studies. Without them, the scientific rigor of hundreds of thousands of research experiments would come under scrutiny. The simple reason for this is a phenomenon called:

The Experimenter-Expectancy Effect

This effect (also known as the observer expectancy effect) is a psychological effect which causes an experimenter to subconsciously affect the results of an experiment.Double Blind StudyHow could that happen, you ask?

Well, let’s say I was to run an experiment in which I’m trying to find out whether people with black hair prefer lobster mac and cheese over a plate of steamed broccoli. Now let’s say you and I look a lot alike.

NOW let’s say I’m a BIG fan of lobster mac and cheese. (Trust me, this is important)

Under those circumstances, the experimenter-expectancy effect would dictate that I have a subconscious belief that you’re going to love the lobster mac. As soon as I walk into the room to ask you which dish you prefer, I subconsciously decide that I want YOU to eat the lobster mac and cheese. Notice that I say “subconsciously.”

As the experimenter, I have every incentive to achieve scientific rigor in my experiment. My preference for one dish over another should have no effect on the results of my experiment. What’s more, my conscious mind believes that.

My subconscious mind, on the other hand, sees your face and is already making thousands of tiny connections between your face and that delicious lobster cheesiness. So when I walk into the room, every element of my body language, speech, eye movement, and other factors under my non-conscious control are pushing a preference for the lobster mac and cheese.

So when I ask you the question:

“Which dish would you prefer…”

This is what I hear:

“Steamed broccoli or lobster mac and cheese?”

But this is what actually comes out of my mouth:

“Steamed broccoli.. ORRR… Delicious, cheesy, warm, gooey lobster mac and cheese???” *wink* *wink* *wink*

All the while, my conscious mind as the “very professional experimenter” is thinking nothing but “I wonder what they’ll choose…” Obviously I’m exaggerating a bit, but the effect does come across, and unless you’re lactose intolerant or hate shellfish, you’re probably going to have a preference for the warm cheesy gooeyness.

Adding In The Double Blind

A double blind study changes all of this.

In a double blind, the identify of the participant (meaning whether you are in the control group or test group) is hidden to not only the participant, but also the researcher. That means that you don’t know whether we’re testing against hair color, weight, gender, or anything else. And even though I might still have a preference for the lobster mac, under double blind conditions, I wouldn’t see your face.

Since physical appearance is a variable in the experiment, knowing your physical appearance would open up the possibility of me presenting the two food options differently as a result of your hair color. Under this double blind, I wouldn’t know who I was talking to, much less what you looked like, so my subconscious mind would draw no conclusions to whether you should or shouldn’t choose the lobster mac.

(If we took this one step further and applied normal scientific rigor to the experiment, I would be fired and replaced with a simple piece of paper with two big check boxes. Just saying.)


Double blinds introduce a uniformity to research results which would otherwise have been exposed to non-conscious, subjective, and unrecognized biases on the part of the researchers. If a study has not been conducted in a double blind (or triple blind – those exist too) fashion, there had better be a good reason for it. Otherwise the results of that experiment could be invalidated due to the experimenter-expectancy effect.

Double-blind it, baby!

Stay Brilliant,