Chapter 7 selection of variables, operational definitions, and. An independent variable is the variable in a study we manipulate. A dependent variable is the variable being measured. Levels of the independent variable - the number of conditions for a specific independent variable e. g. , low birth weight & normal birth weight. Multiple dependent variables - having more than one dependent variable i. e. , to increase the amount of information collected. Floor effect - when scores fall primarily at the lower range of a response option e. g. , most students getting below 20% on a certain difficult test. Ceiling effect - when scores fall primarily at the upper range of a response option e. g. , most students getting above 80% on a certain easy test. Operational definition - defines how a concept or idea will be measured (not defining a concept) i. e. , to make a broad concept more specific.