Suppose we do a study looking at the age of marriage and the likelihood of divorce in the years following the marriage. We gather data from thousands of men and women. To account for this finding, we would draw on some theory, perhaps one that younger people more readily follow their impulses and do not think through the consequences of a course of action. The theory would come out of their experience, their observations of people they knew at different ages, and how they approached marriage. The statistical, quantitative information we gather in research studies is meant to extend that observation and show its generality, or to correct it when it has been wrongly interpreted.
Observation lies behind all research.
Observational studies, such as case studies and fieldwork, make the observation more systematic and complete. They precede and comple ment large-scale quantitative studies. They are really, or should be, the core studies, which the larger studies serve to certify. Unfortunately, many start with a large scale study, because the data are available, or the funds are there to make the data available, and work back using their casual observation and experience, or common knowledge, to suggest what to look for or to interpret what they have found. It is also interesting that many large-scale studies are required to go to great lengths to establish and improve the validity and reliability of their measures, because the data they use are often records of casual observation.