In General

Validity asks the question, "How do we know what we know?" Every field of study answers that question differently, but there are some ideas that are generally considered invalid, no matter whether an information source is scholarly or non-scholarly, and no matter what discipline or subject area it falls under.

In an earlier section, we talked about how the intended audience and purpose of an information source can slant the information in it. The concepts of ideology, agenda and bias are related to that. 

• Ideology is a belief system shared by a group of people. Religions, political groups, and advocacy groups have ideologies. Not all ideologies are bad. And just because an author subscribes to an ideology does not mean that the information source necessarily has an ideological agenda. 
• Agenda is a set of goals shaped by an ideology. If an information source has an agenda, that means it is not strictly informational or educational. It is probably actually a persuasive information source or a piece of propaganda, even if it is pretending to be otherwise.
• Bias is the tendency of an information source to selectively over-emphasize some things and de-emphasize other things in such a way that it unfairly favors a certain conclusion or point of view.

A credible information source will not try to tell you how to feel about the information.

By Discipline

Humanities

Literature, the arts, history, philosophy, theology...

In the humanities, the author is either constructing a worldview, or (more often) adding to, refining, and correcting a worldview that other scholars have created. That worldview needs to be self-consistent and consistent with the evidence. It needs to be able to support new discoveries and insights. And it often needs to be beautiful. 

Here are some criteria for validity that can be generalized in the humanities:

• Good use of primary sources. Appropriate sources are chosen. They are translated and interpreted correctly. Provenanceis clear. 
• Anecdotes are fine as long as the author makes it very clear how they represent general principles. 
• Drawing connections and creating a persuasive (and beautiful) argument in favor of them. 
• No logical fallacies.
• Exhaustive knowledge of relevant secondary sources, both the ones who support the author's arguments and the ones who oppose them. Addressing and participating in the multi-threaded conversation among thinkers is very important in the humanities. 

Social Sciences

Psychology, sociology, anthropology, linguistics, economics... 

The social sciences try to explain human minds and human societies using scientific method, but they are limited in how they can apply scientific method because of the practical and ethical problems that arise when you try to experiment on or observe human beings, communities, and cultures under controlled conditions. 

• As with the humanities, social science criteria for valid information sources include a good background in the work of other scholars in the subject area, and no logical fallacies. 
• Statistics are very important for deriving measurable information from the inputs. A valid social science information source will tell you exactly what statistical instruments were used and will present not only the numbers, but also a measure of how certain those numbers are (standard deviation, plus or minus language.) 
• Research methods are very important. A valid social science information source will have a whole section that describes methods, and will address things like how the sample was selected, how representative the sample was, and how variables were controlled for. The weaknesses and ambiguities will be addressed.
• Avoiding bias - usually unconscious - on the part of the experimenter/observer, or in the responses of study participants - is very important. 

Sciences 

Mathematics, physics, chemistry, biology, earth science, astronomy, environmental science...

The sciences pursue data about natural phenomena, with the goal of formulating theories that explain and predict those phenomena. 

• Just like the humanities and social sciences, a science information source should include a good background in the work of other scholars in the subject area, and no logical fallacies.
• Scientific validity requires that the claims be generalizable (externally valid), reproducible and falsifiable. 
• Issues of metrology come up in the sciences - how accurately and precisely were they capable of measuring? How much can we trust their instruments? Were they actually measuring what they thought they were measuring?
• Scientific research methods are extremely rigorous, even compared to social science methods. This is because scientific studies focus on phenomena that can be measured with much less ambiguity. No allowance is made for extra variables. 
• Just like the social sciences, a science information source needs to avoid bias and use good statistical and research methods. 

Applied Fields

There is probably an applied field for every academic field. Especially consider business, engineering, computer science, nursing, education... 

The applied fields are all about carrying out the activities of the everyday world. In the applied fields, consider the criteria for validity that are used by the related academic disciplines. In education, consider the validity criteria for psychology and sociology. In engineering, consider the validity criteria for chemistry and physics. 

Also bear in mind that the applied fields are practical, and so they care about what works in practice.

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