I have taken some tests for Asperger's which gives a rating point, and the higher you score its more likely that you have asperger. I was just wondering if this means that there are degrees of asperger, that everyone is asperger to some degree, or is this rating just a property of the test, and people either have asperger syndrome or not?
Whatever test you took, it does not test Asperger. It tests for symptoms that are typical in someone with Asperger.
For example one Asperger test asks you to rate the following statement (translated from German) on a skale from 1 = "totally disagree" to 4 = totally agree":
Now of course people with Asperger often tend to stay by themselves and undertake things alone rather than with friends, but many non-Asperger people might feel that they sometimes enjoy time alone also, for example if they are naturally shy and find being with others enjoyable but exhausting, or if they have a job dealing with people and they like to have some free time by themselves to relax from the constant interaction.
Just this weekend I read an interview with one of the most influential German movie directors, Doris Dörrie, who said how she likes to go on holidays by herself, especially to foreign countries where she cannot interact with anyone because she does not speak the language, and she goes on to tell how she went to Japan and enjoyed her aloneness tremendously and spent whole days basking in being outside society and looking on. Totally Asperger, if you think about it. But her job is to intensely interact with people, and she simply needs time off from that.
It's totally unremarkable that many people show some of the behaviors or emotions that people with Asperger (or other psychological disorders) show. It does not mean that they have Asperger to some degree. Rather, if someone rates very high in that test, that is merely an indication that they very likely have Asperger. No psychological diagnosis relies purely on a single self-report measure, but on a complex series of observation, interviews, and a battery of tests.
Also see the answer by Eoin for a different perspective on the question.
Two additional points to the previous answer from
Autism (and Asbergers) is characterized by a 'triad of impairments' to social interaction,communication (less so for Asbergers), and flexible imaginative functions (i.e. repeated/stereotyped behaviours and interests). Obviously, these are traits that vary across the general population as well (I, like many scientists, can be very focused and one-track in my interests).
I recently also came across a paper by Happé and Ronald (2008) (link) arguing that, genetically speaking, these traits vary independently of each other in the general population. It's only when someone has high levels of all three that they are diagnosed as having Autism.
Finally, for an even more broad theory of Autistic traits in the general population, take a look at Simon Baron-Cohen's extreme male brain theory of autism, which states that people differ in the fundamental trait of being either 'empathizing' or 'systematizing', with men tending to be more 'systematizing'. Autism, then, is just a case of being more like a male brain then usual, or super-systematizing.
I hope this is some help!