If you remember your basic statistics, the mean is the average salary for the job title. They take all of the salary numbers supplied by respondents, add them up and then divide by the number of respondents. Here's one instance where a limited sample size can really affect the outcome. The median is the middle of the pack - where half of the responses are above and half fall below. You make the call.
Bigger companies tend to pay salaries in line with the norm.
Obviously, the more particular a company is about skills and experience, the more they're going to have to pay. The last element you need to consider is the difference between salaries in various regions of the country. If you're looking at a national survey, all of the regional differences have been homogenized out of the data. This can result in an overly optimistic view in one area of the country, or an underreported view in another. Of all the private salary surveys I've seen, the most granular is the one done by Computerworld .