Experiment Design Terminology

Experiment
A planned, organized method to test a prediction, an inference or an explanation.
Manipulative experiment
When the experimenter actively changes (manipulates) the experiment variables. This is usually what people think of when you say "experiment".
Observational experiment
If the scale of the observations or ethical issues preclude the experimenter from making changes, then observations of different situations or reactions to natural changes are made.
Manipulated variable
The variable that the experimenter changes. Also called the independent variable.
Levels of manipulated variable (treatments)
The actual amounts or values the manipulated variable will take on. Also called levels of treatments or just 'treatments'.
Responding variable
The variable that the experimenter will measure. This variable responds to the variable the experimenter changes. Also called the dependent variable.
Controlled variables
The variables that the experimenter keeps constant during the experiment. Also called the constants.
Hypothesis
A possible answer to the question, an explanation.
Experimental Control
An experimental situation or special group of test subjects (the controls) that has nothing done to them. The controls will be used for comparison at the experiment's end.
Quantitative measurements
Data gathered that are referenced to a standard (usually numbers and units). Examples include age, distance, time, temperature.
Qualitative measurements
Data gathered about characteristics or qualities. Examples include color, taste, texture.