esearchers, especially quantitative researchers, fi nd it useful to think in terms 
of variables.The researcher could use a standardized achievement test, a teacher-made test, 
grades in science class, or evaluations of completed science projects.In a study concerned with 
the relation of vocabulary level to science achievement among eighth- graders, 
the variables of interest are the measures of vocabulary and the measures of 
science achievement.Researchers study variables and the relationships that exist 
among variables.