Validity and Reliability

It's become something of a fad lately for instructors to have their students create and upload Youtube videos as class assignments; this one from the University of Texas does a pretty good job explaining the concepts of validity and reliability:



To recap in a nutshell, a valid instrument measures what it is intended to measure while a reliable one yields the same measurement outcome every time it's used. Also, while they sometimes go hand-in-hand, validity and reliability in fact vary independently of each other, as this target shooting analogy suggests:

So, why is all this relevant to public opinion?

As I've noted before, public opinion polls are essentially an instrument or tool we use to measure public opinion. Like all measuring devices, the results they produce may or may not be valid or reliable. Indeed, because so many factors go into designing and executing a public opinion poll -- selecting a sample, writing up a questionnaire, administering it, and analyzing the responses -- there's a lot of room for invalidity and unreliability to creep in. And, while the polling industry has made considerable strides towards improvings polling results over the last half-century or so (see the Zetterberg article from Topic I), they're still far from having perfected their craft.

The remainder of Topic II will be devoted to considering various sources of potential inaccuracy in public opinion polling -- ranging from lying respondents to problematic questionnaire design and poll administration -- and identifying some steps pollsters can take to avoid or overcome these pitfalls.