Availability bias is a mental shortcut for decision making that uses what comes to mind based on your impression, i.e. examples that are easily available to you to visualise. The following puzzle from Tversky and Kahneman is a nice one to illustrate this.
Look at the above two pictures and draw structures starting from the top row to the bottom by passing through one and only one X in a row. If you are not entirely sure about the task, let me illustrate it with examples. The following picture gives one such construction on each.
What comes to mind
If your answer is figure 1, then you are not alone. 46 out of 56 participants thought figure 1 has more paths than figure 2. Their median estimate was 40 in Fig 1 and 18 in Fig 2.
A permutation problem
It is a permutation problem that doesn’t need any guessing. Fig 1 calls for 8 ways to draw connections, 3 at a time or a total of 8 x 8 x 8 = 83 = 512 possibilities. The second one? Well, 2 ways, 9 at a time, 29 = 512 (2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2)!
