Orion :
Expertise can only be attained in a field where there are no variables.
If that was the case then no fields will allow experts. All work done involves sources of error and thus will see variation from one trial to the next. You can reduce them amount of variance in your results but it cannot be eliminated. Some of the most precise work done today is done by the people working in the standards labs. I have worked with them and was left basically in awe at how complete their work was. They will completely take apart and setup up all experimental equipment including full calibrations, multiple times in order to fully guage the uncertainties in their results. This being said, their results are not exact, nor do they claim them to be. They are just as precise as they can make them.
What is important is not how much the error is, but to know very well how large it is. If this is known, and only when this is the case, meaningful statements about cross validity can be made. This is one of the things that makes an expert, they will know very well the strength of the information they know and thus they can make quantitative comparisons based on it. The other thing that would make someone an expert is the ability to learn and grow. Sure you have to know the current information and how it applies to the standards as they exist now, but if you are unable to adapt and extrapolate this information in new situations your abilities are very limited compared to someone who can. Last of all, I have never met an expert who described himself as one.
As a couple of examples, Joe Talmadge is an expert on knife geometry. I have discussed details about cutting performance with him in the past and he was able to make educated guesses about the performance of knives he had never handled by extrapolating his experience. He was also able to discuss where variation could be seen and guage the probable magnitudes. As well note he is always involved in the latest work being done by people involved in this area and updating what he knows.
Bill Martino is an expert at many things, khukuris, moderating and selling his products. These things are all closely linked together. He has assembled a wealth of information about khukuris from being involved with the makers for quite some time, this information is always growing because Bill encourages his customers to work with their blades and is always interested in hearing about them. This is closely linked to why he is so good at selling them. You quickly develop a sense of trust because he is as open an honest about them as can be. He works well as a moderator for precisely the same reasons. I asked him well over a year ago if he would describe the abilities of his khukuris to me before he bought one, his reply was that I was better off talking to his customers to insure an unbiased approach. This was one of the things that impressed me most. It is the same attitude that makes him an expert at moderation, his easy going attitude promotes the flow of information and the feeling of oppression is never there.
-Cliff
[This message has been edited by Cliff Stamp (edited 29 September 1999).]