Sunday, June 24, 2007

Art and Science in Trading and Psychotherapy

Note: The following is my post to an online discussion group that had taken up the issue of art vs. science in trading:

The art/science debate/dichotomy has dogged the field of psychotherapy as well. There we've seen two stances taken toward reconciliation. The first is to identify effective treatments from controlled outcome studies and then create treatment manuals around these. Practitioners are then expected to follow the manuals with fidelity, so that treatment remains "evidence based".

The second approach is to assess outcomes among practitioners who employ subjective methods in talk therapy, relying on clinical judgment and experience. Those studies find that some therapists are consistently more effective than others, that much of their efficacy is independent of the specific treatment approaches they take, and that much of their efficacy is wrapped up in their ability to forge positive working relationships with patients.

In the first instance, insurers attempt to steer patients toward evidence-based approaches to maximize outcomes. In the second instance, insurers attempt to steer patients toward practitioners with the best outcomes. Both represent attempts to bring science to bear in a field that is highly discretionary and subjective.

I believe we see the same thing in the trading world. At hedge funds that I work for as a psychologist, we see a first approach, which is the development of automated trading systems based upon backtested historical patterns in the markets. These address the need for scientific money management by eliminating as much of the human element of trading as possible. Their mechanical trading systems are the equivalent of the therapist's evidence based treatment manual.

The second approach taken by the funds is the collection of copious metrics on traders who employ discretionary judgment. From these metrics, it is possible to determine which traders are achieving results beyond their peers and beyond what would be expectable by luck. Just as insurers track the risk-adjusted outcomes of practitioners and determine, say, who are the best heart surgeons, funds similarly trace the outcomes of their discretionary traders and allocate more capital to their all-stars.

Both of these modes strike me as legitimate applications of science. I don't think all psychologists need to work from treatment manuals, and I don't think all traders need to trade backtested systems. If, however, those psychologists and traders make claims of efficacy, the burden of proof is upon them (and the assessment of their objective outcomes).

Note that even once discretionary practitioners are found to be efficacious, that doesn't necessarily mean that they are successful because of their chosen orientations (Freudian, behavioral, etc.). Indeed, studies have found that specific orientations account for only about 10-20% of outcome variance. Specific practitioner skills and characteristics of patients account for far more variance in outcomes.

Similarly, I suspect that whether a successful trader adheres to one form of TA or another or some other analytical method accounts for surprisingly little variance in P/L outcomes. Specific trader competencies and characteristics of markets being traded may well account for the lion's share of profits. But these are meaningful questions and raising them can only further the cause of science in trading, even as it refines discretionary practice.

Added Note From Dr. Brett: Once we treat traders as trading systems and objectively measure their performance, the dichotomy between what is scientific and subjective falls away. Subjective methods in trading, as in psychotherapy, are objectively valid if they can be shown to produce results beyond those expectable by chance.