Renáta Németh, Dávid Simon
The aim is to further investigate the relationship between two variables by involving a third variable, the so-called control variable
(In Babbie this is under ’ The elaboration paradigm’)
As we saw in the first lesson at Simpson’s Paradox, the relationship between ’Company’ and ’Employees Hired by Ethnic Background’ changed if we also looked at ’Level of Education’ as a control variable.
Also, the relationship between ’Frequency of seeing a Doctor’ and ’Smoking’ would weaken or disappear if we involved ’Gender’ as a control variable.
The objective of using a control variable may vary according to its position in the causal relationship:
explaining an apparent relationship (smoking vs seeing a doctor)
finding an intermediary relationship
discovering an extra influence