deviation from average on a scale from 1 to 100 (personality test) Note: Im not sure Im using the proper "Math" term here in deviation, it is what google translate gives me for the dutch "Afwijking"
I got this question from my father in law who took a personality test to take a look at how his scores were calculated. In this test his personality traits and such are displayed as graphs/bars , to be read from the "middle", but give a result from 0 to 100 later in the test. (or -50 to + 50)
The test (in dutch) claims these values are calculated as "the difference between you and the "norm" (the dutch working population)
Q1 I was wondering how one would get such a value?
Given the norm (1-100) and a score (1-100) how do you get a deviation from average on a +50/-50 scale
Q2 Say the average person has a score of 30 in a competence, and you have 15, would you get a score of 25%//25? and what if you get 60? does that give you 100%? and > 60?
example of "bars"
 A: Per your request, here's an answer.
Q1:
They presumably use percentiles as I said in my comment. Basically, you take a sorted list of $N$ values and see how many of those values (as a percentage of $N$) are less than a given value $V$. If, for example, $80$% of the values in the list are less than $V$, then $V$ is at the $80$th percentile.
It should be mentioned that there is no universally agreed upon definition of percentile (the Wiki link has several variants), but these variants are only really of interest for small $N$.
Q2:
If the "average" person had a score of $30$ in a competence, that would just mean that the $50$th percentile was $30$. Theoretically, all values in the list could be $30$ and thus the $100$th percentile would also be $30$. 
However, talk about an "average" person implies a very large $N$ and furthermore implies a normal distribution. Which leads me to an answer to your question in the comments, namely:  "Would this neccecitate having a vast database of (sorted) anwers per question for each person in the dutch population for their claim to be true?"
The answer is no. If they had a sufficiently large database of answers, and therefore a sufficient sample size, they could make reasonable assertions regarding the population as a whole. 
I, of course, have no idea if this is how they do it. But it is a way that a reputable company could do it. 
