The independent variable in an experiment is called a factor and the different conditions that it takes are levels . In this study Learning Condition is a factor which takes 5 levels. Learning Condition Counting Rhyming Adjective Imagery Intentional Blocking Control the effects of some outside variables by bringing them into the experiment. Block what you can and randomise what you cannot. Eysenck Memory Experiment .
Age has an important effect on memory.
The age of the subjects is the blocking variable. Make 2 or more observations on each subject. The Gastric freezing experiment is a simple repeated measures design. Repeated measurements on an individual are related through being made on the one individual. In a repeated measures design, each subject becomes a block and the experimental units are the subjects at each particular time.