Chapter Four. Research Design: Causation
THE LOGIC OF NOMOTHETIC EXPLANATION
Criteria for Nomothetic Causality
False Criteria for Nomothetic Causality
Necessary and Sufficient Causes
This section of the chapter deals with the topic of
causation: causal relationships among variables. We begin with
the three fundamental criteria for us to conclude that one variable causes
another, such as saying that increased age causes greater religious involvement.
First there must be an empirical correlation
between the two variables. If young and old people were equally religious,
then we couldn't say there was a causal relationship, since there's no relationship
at all.
The second criteria has to do with time order:
the cause has to happen before the effect. In our present example, age
is logically prior to religious involvement. We can imagine that something
about growing older could make someone more religious, but your level of
religiosity can't change your age.
Finally, there's no third variable that can explain
away the original relationship as spurious or non-genuine. Several
examples in the chapter will illustrate this possibility.
Having looked at the criteria for causal relationships,
we'll look at some false criteria that sometimes confuse students.
For example, there does not need to be a 100% relationship between two
variables for us to conclude a causal relationship occurs. That is,
contradictory cases, such as an elderly atheist or young priest, do not disprove
the overall relationship.
In this context, we'll see the difference between necessary
causes, which must be present for the effect to exist, and sufficient
causes, which also cause the effect to exist.