By Andy Cotgreave, Technical Evangelism Director

Did you think of a card like I asked on Twitter? If you haven't yet, pause here and think of a playing card. Stick with the first one you think of.

Using my powers of magic, I wanted you to choose one of the five I preselected. Was your card one of the five in the image below?

If I was right: You're amazing and felt the magic power in the tweet.

If I was wrong: I blame the data!

In my spare time, I am a magician. Yes, if you meet me at a conference or event, ask me to do a magic trick. I'll be happy to show you some stuff. I got into magic as a direct result of studying data visualisation. In data viz, we exploit the POWER of our cognitive abilities while in magic, we exploit the weaknesses of those same systems. Learning about one always informs the other.

I've recently learnt that magicians use data to help craft effects like this one. Jay Olson is a psychologist at McGill University in Canada. He studies the psychology of magic. One of his best-known experiments was to consider whether people like some cards more than others. And if they do, he could use that knowledge to force a particular card on an audience.

It turned out people do favour cards, and how you ask the question determines which cards are most likely to be chosen. He's asked thousands of people the same question I asked you in the tweet, and made that data available for everyone. I explore this data in Vizable and use it to help me craft ways to force you to think of particular cards.

For example, the most-liked cards are ace of spades, queen of hearts, ace of hearts, king of hearts, and jack of spades. In fact, if asked people to "think of a card," 50 percent of those people pick one of the five cards in my picture above. Jay calls this "verbal accessibility." Here's the chart I used to help me craft the Tweet trick:

At the other end of the scale, the least-likely card to be thought of is the nine of clubs. Knowing the most- and least-likely cards is very useful to a magician.

The way I frame the question is also very important. If I'd asked you to "visualize" or "picture" a card, you may have picked something else. For Jay, this second type of questions is "visual accessibility." I added that to the chart (in the column titled "vis acc"). The top cards are similar but there's interesting difference. When asked to picture a card, the ace of hearts is more commonly picked than the ace of spades.

Clearly, how I word my questions is important, too.

What if I showed you a selection of cards and asked you afterwards to remember one you saw? It turns out the ace of spades has the highest "memorability sensitivity" ("mem sens" in the chart below), followed by the aces of hearts and diamonds, and then the eight of hearts.

The aces are kind of obvious, but if I mixed the eight of hearts with the cards at the opposite end of the spectrum, I'd be quite confident which card you would pick.

Knowing that 50 percent of people will pick one of four cards is very powerful for a magician. You might think probabilities aren't strong enough for magicians. If I ask the question and you choose the card I want to continue with, then, obviously, I'm onto a winner and can pull off an incredible effect.

However, you might think that because it's not guaranteed that you will say the card I want you to say, that I'll be in trouble. Well, magicians are crafty, and there are many tricks we have up our sleeve (sometimes literally!) to get out of that problem. Unfortunately for you, reader, those tricks are out of the scope of this post!

Finally, please fill out this form. Tell me if you picked on the four cards. If not, which card did you pick?