Here we'll examine some fundamental principles about conducting empirical research: causation, and variations on who or what is to be studied, when and how. We'll also take a broad overview of the research process.
Explanatory scientific research centers on the notion of cause and effect.
Most explanatory social research uses a probabilistic model of causation. X may be said to cause Y if it is seen to have some influence on Y.
X is a necessary cause of Y if Y cannot happen without X having happened. X is a sufficient cause of Y if Y always happens when X happens.
Three basic requirements determine a causal relationship in scientific research: (1)
The independent variable must occur before the dependent variable, (2) the
independent and dependent variables must be empirically related to each other, and
(3) the observed relationship cannot be explained away as the effect of another variable.
When scientists consider whether causal statements are true or false, they are concerned with the validity of causal inference.
Four classes of threats to validity correspond to the types of questions researchers ask in trying to establish cause and effect. Threats to statistical conclusion validity and internal validity arise from bias. Construct and external validity threats may limit our ability to generalize from an observed relationship.
A scientific realist approach to examining mechanisms in context bridges idiographic and nomothetic approaches to causation.
Units of analysis are the people or things whose characteristics researchers observe, describe, and explain. The unit of analysis in criminal justice research is often the individual person, but it may also be a group, organization, or social artifact.
Researchers sometimes confuse units of analysis, resulting in the ecological fallacy or the individualistic fallacy.
Cross-sectional studies are those based on observations made at one time. Although such studies are limited by this characteristic, inferences can often be made about processes that occur over time.
Longitudinal studies are those in which observations are made at many times. Such observations may be made of samples drawn from general populations (trend studies), samples drawn from more specific subpopulations (cohort studies), or the same sample of people each time (panel studies).
Retrospective studies can sometimes approximate longitudinal studies, but retrospective approaches must be used with care.
The research process is flexible, involving different steps that are best considered together. The process usually begins with some general interest or idea.
A research proposal provides a preview of why a study will be undertaken and how it will be conducted. It is a useful device for planning and is required in some circumstances.