Reliability and Validity

Two big concepts-- Reliability and Validity

Without question, in order to understand effective social science research (or any kind of scientific research), you have to understand the concepts of "validity" and "reliability."

To put it simply, "validity" refers to whether a measure actually measures what you purport to be measuring.

For example, if you create a concept called "television use" and then decide to measure it by asking people how many TVs they own, that MIGHT be an indicator of how much TV they watch, but you definitely have some validity problems, right? Why? (post your thoughts as a comment to this entry).

It would probably be better to measure the concept by asking people how many hours of TV per day they watch, on average (or better still, you might have them go hour by hour thinking only of yesterday and to report what they watched during the day).

I'm sure you can see that using a measurement like this is better than just asking how many TVs someone owns...

Reliability, meanwhile, simply refers to how often you can repeat the measurement and get the same result.

Let's take an example and put the two concepts together--

Suppose you have a digital bathroom scale and you step up on it and weigh yourself and it reads "145 lbs."

Now let's suppose you repeat that process ten times in a row and you get results like this--

1. 145
2. 144
3. 144.5
4. 145
5. 145.1
6. 144.5
7. 144.8
8. 145.2
9. 145
10. 144

Acting reasonably, we should see these results and say "this scale has come pretty close to giving me the same reading 10 times in a row, so I conclude it's reliable." If so, its "reliability" is strong and is not in question.

What we do not know, however, is if the scale is RIGHT. What if it's wrong by, say, 10 lbs. and you REALLy weigh closer to 155 lbs.?

The scale's readings are reliable, but we can't say for sure if the scale is valid.

To confirm that the scale really is measuring pounds, we might "test" it by weighing other items whose weights we already know. For example, a 10 lb. bag of potatoes, a weight (from a weight room) of 25 lbs., a 50 lb. bag of rock salt, the official rod of steel used as the standard to determine a "pound" and so on.

Now, if we weigh all those items and each time the scale gives us readings that are really close to what we should expect, we can conclude that the scale is indeed valid.