The independent variable is those variables that can be manipulated by an experimenter. It is opposite to the dependent variable. The effect can be seen through the manipulation in the independent variable on the dependent variable.
So that here in the above context if you want to find out that using cells during driving cause accident. The cell phone will be here as an independent variable. Because when cell phone manipulated it will show the effect of the accident. It depends on the cause and effect relationship.
The processing-speed theory of Adult Age Differences in Cognition is a theory that suggests that as age in adulthood increases in human, there is a corresponding decrease in the processing speed of many operations executed, which results to impairments in cognitive functioning because of the simultaneity and limited time mechanism.
