Excellence in Autobiographical Statements
Please keep in mind that, while it may seem to you that the reason you are interested in your field is that you want to help people, this reason has become a terrible cliche and should be avoided. The problem is that it adds little information. If I were to have the privilege of helping you with your autobiographical statement, I would ask you a series of incisive questions so that I would have all of the required building blocks of your story to work with. Perhaps there is some particular kind of human problem that evokes your desire to be helpful--maybe you are particularly interested in helping emotionally disturbed children, or possible the aged, or the disabled. In addition, this will allow you to couple your emotional motivation with the serious intellectual interests you may have. If you are a scientist, you might want to think in terms of paradigm shifts that coincide with life stages, what you were thinking about 5 years ago, 10 years ago, etc.
Try to focus on particular educational and occupational experiences you have had that could account for your interests, rather than personal experiences. For example, it is probably unwise to say that you are interested in the neural basis of depression because you want to find out why your father became depressed and had to be admitted to a mental hospital. Such personal experiences are difficult to put into a short written statement without either trivializing them or needlessly confining your intellectual interest to emotional motivation. It helps to think of your audience. Who will read this statement? It will be read by academic psychologists who have dedicated their career to scholarly endeavors. Scholars rightly distrust too much personal motivation entering into science because it can lead to a distortion of the scientific process. They are looking for the kind of motivation they themselves either have or wish they would have--an intrinsic and serious interest in the substance of the issues dealt with. Try to share experiences that reflect on that part of your reasons for seeking graduate level training. If you cannot find such reasons, perhaps now is a good time to think about whether a career in science is for you.