An experiment's validity can be threatened by the presence of which type of variable?

The presence of extraneous variables can threaten an experiment's validity because these are uncontrolled variables that can affect the outcome of the experiment, leading to confounding results. When extraneous variables are present, they can introduce noise into the data and make it difficult to determine whether it is the independent variable that truly causes changes in the dependent variable or if those changes are due to other factors.

Extraneous variables can come from various sources, such as the environment, participant characteristics, or measurement methods, and they need to be identified and controlled to ensure that the results of the experiment are accurate. By minimizing the influence of these extraneous variables, researchers can enhance the ability to draw causal conclusions between the independent and dependent variables, thereby increasing the internal validity of the study.

In the context of the other variables mentioned, the independent variable is the one being manipulated to observe its effect, the dependent variable is the outcome being measured, and control variables are those that are kept constant to prevent interference in the results. Thus, while the independent, dependent, and control variables play critical roles in an experiment, it is the extraneous variables that pose a specific threat to the validity of the findings.