Why use 4 Smiley faces?
No middle button = No unreliable results
There's proven psychology behind giving the choice of 4 smiley buttons rather than 3 or 5.
Human Nature shows that people will take the easy option if there's one available.
As an example, when giving an online review for something and asked to score between 1 - 5, how often do we press the number 3 button? Lots of times is the answer, and for the company asking for feedback, that tells them nothing of value.
For that reason, at HappyOrNot there will always be 4 smiley faces to choose from: