In this video I introduce psychometrics, the study and design of testing for traits and abilities. I describe the difference between power tests and speed tests for assessing intelligence and the importance of differentiating people in order to have a worthwhile test. Next I describe the difference between an achievement test and an aptitude test and how this relates to Raymond Cattell’s distinction between crystallized intelligence and fluid intelligence.

Don’t forget to subscribe to the channel to see future videos! Have questions or topics you’d like to see covered in a future video? Let me know by commenting or sending me an email!

Check out my book, Master Introductory Psychology, an alternative to a traditional textbook: http://amzn.to/2eTqm5s

Video Transcript

Hi I’m Michael Corayer and this is Psych Exam Review. In the previous video I talked about definitions of intelligence and we saw that researchers disagree and debate over which traits and abilities should be considered part of intelligence and which should not be. Now regardless of which definition of intelligence we’ve chosen once we have a definition we want to design an assessment that allows us to assess people for this type of intelligence.

And so this brings us to the study and design of testing for traits and abilities. This is a field that’s known as psychometrics, and so a person who does this type of work would be a psychometrician. Now let’s imagine that we’re designing some sort of assessment for intelligence and one question we might ask is “how difficult should our questions be?” and the answer we might come up with is “well, we want to have a range of difficulties, but we want to make sure we have some very difficult questions.” If all of the questions on our assessment are relatively easy and most people can correctly answer them, then what’s going to happen is most people are going to end up getting the same IQ score and that’s not really what we want. The point of an intelligence assessment is to differentiate people. We want to find the differences between people when it comes to intelligence and so that means if everyone gets the same score then the test is fairly useless. We want to have a test where people get very different scores and there’s fine distinctions between one person’s intelligence and another person’s intelligence. And that may just come down to one particularly difficult question that this person can solve and this person wasn’t able to solve.

So this brings us to consider what’s called a power test. If we’re designing a test and we have some very difficult questions that very few people can answer, that’s going to have higher power. What that means is that it can differentiate people more finely. So we might have one question that, you know, one in a thousand people is able to correctly answer. And that’s going to be good for having what we call power. Now, if we had very easy questions and everyone could answer them, then we would criticize our assessment and say that it has low power.

Now this isn’t the only way we might think about test items. We could say “well what if we have some easy questions but rather than just seeing if someone can solve them, we might see how many of these can they solve in a particular amount of time”. So we can influence some other factor like time and this would be something like a speed test. You might say, ok these questions are relatively easy, most people can answer them, but we’re not concerned with whether or not you can answer the question. We want to see how quickly can you answer. So we might say, how many of these easy items can a person come up with the correct answers to in just two minutes? And then what we’ll find is that even though everybody is able to answer the questions, some people might be able to answer them, you know, twice as quickly. They complete twice as many items as someone else and that might tell us something about their intelligence, right? So that would be a speed test.

Now another thing we can think about when we’re designing assessments is a distinction between achievement and aptitude. So what’s the difference between these terms? Well, achievement refers to knowledge that has been accumulated through experience, right? So it’s a test of learned knowledge. If you have an achievement test, we’re measuring knowledge or skills that have that has been learned. And so hopefully in school most of the tests that you have are achievement tests and that’s because you’re taught some material and then we test your achievement. Have you actually learned that knowledge or these particular skills?

And this is different from an aptitude test because what an aptitude test tries to do is predict potential ability. So it’s not testing what you know now, it’s testing what’s your capacity to learn things in the future? And this is really what we’re looking for in an IQ test, right? We want an IQ test to be able to predict future performance. We don’t want to just measure things that you already know because then obviously, you know, as you get older you know more and more things and your IQ would just continuously rise throughout your life and that’s not really what we’re interested in when we assess intelligence. We want to know about potential for the future. We want to assess children and say this child has very high potential to learn more quickly or learn more things or something like that. So this distinction between an achievement test and an aptitude test: so a test in school that you take would most likely be achievement test you take, you know, in an AP psychology class or something. You’ve learned that knowledge and then they test, you know, how well you’ve learned it. Whereas an IQ test would be an aptitude test.

Now this brings us to a distinction in thinking about intelligence. We might say, well there’s sort of the intelligence for things that you’ve learned and then there’s intelligence for your capacity to solve new problems. And so this is a distinction that was made by Raymond Cattell and he used factor analysis to separate these two types of intelligence. Cattell referred to these as crystallized intelligence and fluid intelligence. So crystallized intelligence would be sort of like the achievement side where it’s knowledge that’s been accumulated through experience. And fluid intelligence would be your ability to solve new problems that you haven’t solved before.

One way to think about this is to imagine playing video games. So let’s imagine and maybe I’m speaking from some personal experience here, but let’s imagine that you’ve spent maybe too much time playing a game like Call of Duty, right? So when you first started playing, you know, maybe the controls were a little difficult. You were learning them and then you sort of mastered the control layout for that game and you’ve learned certain strategies for how to get through particular missions. Now let’s imagine that you start playing a new game but it turns out this new game has identical controls to Call of Duty that you’ve already played quite a bit. Now what’s going to happen is when you first play this new game, you’re actually going to be pretty good at it at the, you know, sort of beginner levels, right? Because the controls are already mastered. You have this crystallized intelligence for how to use this control layout and it’s essentially automated. You don’t even have to think about it.

So you’re going to do pretty well when you first start playing this game and that’s because of your crystallized intelligence. Now let’s imagine that a few levels into this new game there’s different types of challenges that you’ve never had to solve before. You never had to do this type of mission in Call of Duty where you never had to have this particular strategy in order to get through a level. And so now you’re going to rely on your fluid intelligence. You’re solving a new problem that you haven’t solved before. You’re going to have to think about possible solutions and maybe try some new things in order to do this. So that’s one way that you can remember this distinction between crystallized intelligence and fluid intelligence.

Now an interesting thing about fluid intelligence is that it peaks around sometime in your 20s, and then it declines for the rest of your life. Now you may wonder, you know, that might sound very strange and you might wonder “well that doesn’t seem to be the case, I mean people who are older do tend to seem, you know, they don’t seem like their IQ is dropping”. And part of the reason that it doesn’t seem this way is that their crystallized intelligence continues to accumulate and this essentially compensates for the decrease in fluid intelligence that occurs. But because they’re still accumulating new skills they’re acquiring new knowledge that they can use, even though they might not be able to solve new problems as quickly as they could when they were in their twenties.

Ok, so that’s the distinction between crystallized and fluid intelligence and achievement and aptitude and in the next video we’ll start thinking about how we assess our assessments and that means we’re going to be talking about validity and reliability. We want to figure out, “have we made a good assessment or not?”. I hope you found this helpful, if so, please like the video and subscribe to the channel for more. Thanks for watching!