Disadvantages of obsevation in data collection?

Answer 1

Surveys or studies that involve collection of data can be categorized as either observational or experimental. The experimental study occurs in a very controlled environment where some treatment is applied to the subjects. Data collection measures the change in some attributes of subjects after treatment. Wikipedia terms observational studies as "uncontrolled experimental studies." See related link. Observational studies can be more difficult as follows: 1. The controlled environment may be missing. Suppose I am asking people if they like a particular product. Some may have used this product, others may have heard bad things about it from friends. The influences can be numerous. 2. The means of obtaining a representative sample may be complicated. Suppose I am interested in determining if a particular pollutant is causing any harm. I would go to an area where the pollutant was the highest and examine people complaining of problems. Perhaps other pollutants are higher in this particular area. I have confounding problems. 3. The observational study often suffers from an inability to do "identical, repeated trials" as it does not initiate a particular treatment. This inability can result in erroneous conclusions, particularly when data is scarce and develops over time. This is particularly true in epidemiology studies, where the area to be studied and the time required to reach a conclusion depend on the phenomena being studied. If the disease is changing with time, it may be impossible to reach a conclusion even after many incidences have occurred. Does this mean we should just rely on experimental data? No, because in many areas which involve spatial analysis (astronomy, mining of minerals, epidemiology), experiments are not possible. Many disease studies depend on both experimental data and observational surveys.