1.4.2 - Causal Conclusions

In order to control for confounding variables, participants can be randomly assigned to different levels of the explanatory variable. This act of randomly assigning cases to different levels of the explanatory variable is known as randomization. An experiment that involves randomization may be referred to as a randomized experiment or randomized comparative experiment. By randomly assigning cases to different conditions, a causal conclusion can be made; in other words, we can say that differences in the response variable are caused by differences in the explanatory variable. Without randomization, an association can be noted, but a causal conclusion cannot be made.

Note that randomization and random sampling are different concepts. Randomization refers to the random assignment of experimental units to different conditions (e.g., different treatment groups). Random sampling refers to probability-based methods for selecting a sample from a population.

Randomization
The act of randomly assigning cases to different levels of the explanatory variable
Causation
Changes in one variable can be attributed to changes in a second variable
Association
A relationship between variables