Mean Data Security

Here's a simple approach obtaining summary statistical information from a group of honest people, that gives them complete personal data security, from Futility Closet:

My employer has nine workers. The nine of us want to determine what our average salary is, but none of us wants to divulge our own salary. Can we find the average without doing so?

Click through here for the answer.
Of course if one employee chooses to deceive, that one outlier makes this method not very resistant.

Visual Averaging

Designer Moritz Resl constructed a visually averaged alphabetical font by superimposing 900 different font characters with low opacity. See his video here. The full, lower-case average font can be seen here via Design-Milk.