Validity

On Validity, as conceived in social sciences... (extracts from here, an article by Eric Schwitzgebel)

Shadish, Cook, and Campbell (2002) begin with a seemingly clear commitment: validity is a property of inferences. 

Validity is a property of inferences. It is not a property of designs or methods, for the same design may contribute to more or less valid inferences under different circumstances.... So it is wrong to say that a randomized experiment is internally valid or has internal validity -- although we may occasionally speak that way for convenience (p. 34)

Inferences are not true or false. They are valid or invalid. What is true or false are propositions: the premises and the conclusion.

An inference is one thing and a claim is another! Shadish et al., despite emphasizing that validity is a property of inferences, confusingly add they will treat "inference" and "knowledge claim" interchangeably. But an inference is not a knowledge claim. An inference is a process of moving from the hypothesized truth of one or more claims to a conclusion which, if all goes well, is true if the claims are true.

Psychologists' and social scientists' claims about validity, in my judgment, make the most sense on the whole and are simplest to interpret if we treat validity as fundamentally a property of claims or propositions rather than as a property of inferences (or methods or instruments or experiments).

Validity, in the psychologists' and social scientists' sense, is best conceptualized as a property that belongs to claims: the property those claims have when they are true.

I diagnose the confusion as arising from three sources: First, ... Second, a tendency among those who do want to rigorize to notice that the philosophers' logical notion of validity applies to arguments or inferences, and consequently some corresponding pressure to think of it that way in the social sciences too, despite the dominant grain of social science usage running a different direction.