The group also does a wage and salary survey that looks at pay levels in dozens of cities around the country. But its focus is on different occupations rather than salary levels. One of the jobs looked at is administrative assistant, which, according to the Employers Group survey, carries a median salary of $33,222 nationally.

For a moment, let's shift our attention back to the Mercer ranking. The salary differential for Chicago is listed at 10.9%, meaning that jobs for which the national median is $30,000 will pay, on average, $33,270 in Chicago.

Applying that differential to the administrative assistant position, we could assume that in Chicago, the job would pay about $36,843. In fact, administrative assistants at the 86 Chicago-area firms surveyed by the Employers Group on average earn about $43,200.

So the salary differential in Chicago where administrative assistants are concerned is around 30%, or nearly three times the differential for all jobs that pay about $30,000 a year. For anyone interested in this field, this is one of the pleasant surprises to which Cira refers.