A dental sales representative describes the strength of a new ceramic material in Newtons per square metre. This is an example of what type of variable?

Correct answer: C. Continuous

• A. Independent describes a variable's ROLE in a study, not its type — it is the one the investigator manipulates. If this ceramic's strength were being studied, strength would be the outcome depending on material choice, making it the dependent variable.
• B. Categorical (qualitative) variables assign a unit to a named group rather than a number — hair colour, ASA class, Angle classification, blood type. Strength expressed in N/m² is numeric, so it cannot be categorical.
• C. CORRECT. A continuous variable is obtained by MEASURING and can take any value within a range of real numbers, limited only by the precision of the instrument. Material strength in N/m² can be 312.4 or 312.47 MPa — there is no gap between permissible values.
• D. Discrete variables are obtained by COUNTING and take only distinct whole values with nothing in between. The number of teeth in a patient's dentition is discrete: 27 or 28, never 27.5.

Note: Two independent axes, and questions often test both at once. TYPE: numeric (continuous or discrete) versus categorical (nominal or ordinal). ROLE: independent (manipulated, the presumed cause) versus dependent (measured, the presumed effect). A single variable has one answer on each axis.