(FORTUNE Magazine) – As business psychologists we've recently finished a 12-year study of the career paths of over 650 business professionals at all levels and in a wide variety of functions, industries, and organizational cultures. More specifically, we've analyzed how people make career decisions--and what goes into decisions that are satisfying and successful over the long term. One of the most common mistakes we've seen people make in managing their careers is basing their initial (and subsequent) career choices on their aptitudes rather than on their interests. While other personal variables (such as skills and values) and job-market forces (such as the need for Internet-savvy marketers) change over time, a person's deep interests remain highly stable from early adulthood on.

People who are unhappy with their career directions often tell us they chose their career (engineering or financial services, say) based on what they had excelled at in school (math, science, or finance)--but never really liked. Or they made a choice based on one strong interest, only to find that the career involved a lot of work they had no interest in, or no work that satisfied another deep interest they had. The net result is analogous to wearing a pair of poorly fitting shoes: They may be better than no shoes at all, but not by much.

Having gathered extensive data--including comprehensive psychological assessments, in-depth personal interviews, and letters from friends and associates--on those 650 people, we set out to do two things. First, we wanted to determine the essential elements that make up work in business--the irreducible "building blocks." Second, we hoped to develop an assessment instrument that would measure people's interests in those activities. Put another way, our goal was to develop an interest inventory that was fine-tuned to business work--much as turning up the power on a microscope results in a narrower field of view, but with more detail revealed. We eventually developed a sophisticated Business Career Interest Inventory (BCII) and identified the eight core sets of activities shown below on this page as Part 1.

We've devised a brief exercise to give you a rough approximation of your interests in these eight activity sets. The BCII itself, far more analytically complex and nuanced, compares the strength of your interest in each core function to the interest level of other business professionals, assesses your overall interest in business work, and adjusts for your mood at the moment. The exercise shown on these pages does, however, provide some basic clues to your proper career path. To use it, reread the brief descriptions of the eight sets of activities on the previous page, then quickly go through each of the pairs in Part 2 above and indicate which one is more interesting to you by placing the bold letter for that choice on the line to the right. Don't leave any out, and don't mark any ties. Mark only your first intuitive response.

Now sum up the number of times each of the eight functions was ranked higher than whatever it was being compared with, and record that number. Look at your top four scores. If there is a clear "break" (a two-point or greater difference) between the second and third, or between the third and fourth, you should consider the top two (or three) as your most significant interests. If not, think of all four as your leading interests. Most people will have between one and three leaders.

The next step is to match your scores with the career functions listed in Part 3 on the following page. Needless to say, if you look at your interests and see that being a CEO or president is a good fit with your interests, this doesn't mean you're qualified to get those positions tomorrow. What it does mean is that given sufficient experience and the right kind of company, those would be positions you could aspire to and be happy pursuing. If your interests fit a particular combination, consider career paths leading to one or more of the indicated careers. Of course, the results of this exercise can't give you the full picture of your total interest pattern, which is key in making optimal career decisions, but they can give you a flavor for how the model works.

Using our database of business professionals, we have developed interest profiles for several different business careers, against which readers can map their own interest patterns. In this way people can determine how well they match with various career paths in terms of all of their interests. Part 3 shows the level of interest in various combinations of the eight activity sets for an "average" investment banker, general manager, production and operations manager, and so forth.

For example, we see that someone whose response was dominated by interests in Enterprise Control and Managing People may be suited for the corner office as a CEO, president, or division manager. The typical Wall Streeter may prefer to combine an interest in Enterprise Control with a strong regard for Quantitative Analysis. People inclined toward careers in entertainment or the media, meanwhile, may evince a high regard for Creative Production; those who also have a managerial bent may be interested in Enterprise Control as well. And so on.

It's important to note that it is the overall shape of all eight core functions that makes for a good or bad fit with a person's individual profile. If you have a very strong interest in an activity set that most people in a particular career are not at all interested in, chances are that it affords little opportunity to express the interest--and that you may find that you feel quite different from other people in the field. This is just as much a cause for concern as having very little interest in an activity set that most people in the career are very interested in, and that success and satisfaction in that career depends on.

It is also important to evaluate any particular work opportunity thoroughly: The everyday mix of activities of a marketing manager at Procter & Gamble is likely to be rather different from the activities of a marketing manager at Cummins Engine.

The value of this research is demonstrated by the adoption of the model and the BCII by over 40 career-services offices in MBA programs and undergraduate schools in the U.S. and Europe, and by corporate human-resources and career-development professionals involved in internal career self-management programs for their employees. It seems the change in the societal employment contract and the increased mobility of the holders of intellectual capital are combining to give companies an urgent interest in helping valued employees remain optimally engaged in their work. That means providing more help with their choices of a long-term career path.

More career profiles and more detailed interest-scale combination descriptions are available at our Website (www.careerdiscovery.com). As our database grows, we will be posting further research findings at that site.

The authors are directors of MBA career-development programs at the Harvard Business School. They are also principals in Waldroop Butler Associates, a consulting firm in Brookline, Mass., that specializes in career-development consultation to corporations and individuals, and in executive coaching. Waldroop and Butler can be contacted through their Website (www.careerdiscovery.com) or by E-mail at wba@world.std.com.