If you want to conclude that a given variable has a causal relation with a second variable, you have to be able to rule out other possible causal variables. The principle of causation involved here is the -

The correct answer is the Internal validity rule.

Important Points

When concluding that a given variable has a causal relation with a second variable, the principle of causation involved is the internal validity rule.

• Internal validity refers to the degree to which a study or experiment accurately demonstrates a causal relationship between variables, ruling out other possible causal factors.
• To establish internal validity, researchers need to ensure that the observed relationship between the variables is not due to confounding factors or alternative explanations.
• They must control for other possible causal variables and establish a clear cause-and-effect relationship between the variables of interest.

Causal ambiguity rule:

• This is not a recognized principle in the context of establishing causation.
• Causal ambiguity refers to situations where it is difficult to determine the exact cause of an observed effect.

Temporal precedence rule:

• Temporal precedence is an important aspect of causality, stating that the cause must precede the effect in time.
• However, it does not address ruling out other possible causal variables, which is the focus of the question.

 Covariance rule:

• The covariance rule states that there should be a statistically significant association between the cause and effect variables.
• While this is an important criterion for establishing causality, it does not address ruling out other possible causal variables.

Therefore, the correct answer is option 4) Internal validity rule, as it directly addresses the need to rule out other possible causal variables when establishing a causal relationship between variables.