The practitioner aims at applying that knowledge by manipulating those variables for some purpose, e.g., curing an illness. Medicine began as an art form. It evolved as a field when it began observation and theory formulation. Experimentation varies from controlled experiments to qualitative analysis. Depending on the area of interest, data may be hard to acquire.
Human variance causes problems in interpreting results.
However, our knowledge of the human body has evolved overtime. The focus in manufacturing is to better understand and control the relationship between process and product for quality control. The nature of the discipline is that the same product is generated, over and over, based upon a set of processes, allowing the building of models with small tolerances. Manufacturing made tremendous strides in improving productivity and quality when it began to focus on observing, model building, and experimenting with variations in the process, measuring its effect on the revised product, building models of what was learned. There are researchers and practitioners.