• A variable, as opposed to a constant, is anything
that can vary, or be expressed as more than one
value, or is in various values or categories (Simon,
• Quantitative designs have at least two types of
variables: independent and dependent (Creswell,
• independent variable (x-value) can be manipulated,
measured, or selected prior to measuring the
outcome or dependent variable (y-value).
• Intervening or moderating variables affect some
variables and are affected by other variables.
• They influence the outcome or results and should
be controlled as much as possible through
statistical tests and included in the design
(Sproull, 1995; 2004).
• (ANCOVA) may be used to statistically control
for extraneous variables. This approach adjusts
for group differences on the moderating variable
(called a covariate) that existed before the start
of the experiment.