A systematic way of organizing and understanding observations
A proposed relationship between two variables
Anything which can be measured or described along a particular dimension
A variable which can be measured across a continuum, such as weight, time, etc.
A variable with a fixed meaning or attribute (i.e. pregnant/not pregnant)
Label and describe the variables of interest; such as: research on sexual activity and adolescence: how do you define "sexually active"; research on marijuana use and academic achievement (how does one define/differentiate "use"?)