Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: What kind of validity does the degree of confidence refer to, with which it can be inferred that the cause-effect relationships between the variables of an investigation are interpretable in the sense suggested by the researcher?
Options: <1> Internal validity <2> External validity <3> Discriminant validity <4> Ecological validity <5> Construct validity
Output:
1