3. In a series of questions, you will have to choose which...

3. In a series of questions, you will have to choose which bar graph is showing I. One main effect and no interaction II. Two main effects and no interaction III. One interaction and no main effects Here is a sample so you can practice. Match each of the following graphs with one of the three options above. I. One main effect and no interaction II. Two main effects and no interaction III. One interaction and no main effects

Transcript

00:01 A couple different graphs to determine if there is a main effect happening.

00:03 So i want to give you a couple examples just so you can pretty clearly see the yes and the no.

00:08 So for one example, we are going to be looking at here where we have line b1 going up and then b2 going down.

00:23 So in this instance, we want to always start by looking to see, you know, are our lines parallel? and if we look at b2 and b1, we see they are going in opposite directions, one going up, one going down, so they are not parallel, which means that they are interacting.

00:50 So then we would look at, you know, how are these things interacting? well, since one is going up, one is going down, we know they are interacting in opposite directions, but just how opposite are they? for this particular example, imagine that they're, you know, they start at the exact same thing.

01:08 Place here and the exact same place down here.

01:12 And so in this case, they would be, you know, directly opposite of one another.

01:19 When two independent factors are interacting like we see in this first example, that means that they are both changing the dependent variable.

01:31 Both of these independent variables are changing the dependent variable in a way that you wouldn't see if you were to each independent variable separately.

01:43 So because you chose to do both of these dependent variables together, you are getting a new effect on your dependent variable that you would not see if you redid this test with just one than the other.

01:56 So that is how they are interacting, so we would assume that this is probably a significant interaction.

02:02 But then we want to look at, you know, is there a main effect happening? is there a main effect happening with a and is there a main effect happening with b? so with a, what we would look at is the averages at a1 and a2.

02:18 So we're going to look at the domain that is a1 right here.

02:22 Right, we have two different points.

02:24 And so i want to take the average between those two points, which is something like here.

02:28 And i'm going to do the same thing for a2.

02:30 Look at the domain of a2 and then find the average there.

02:33 Once i've done that, i can see that they're pretty equal, meaning that a doesn't really change.

02:40 If we take the average of a, from a1 to a2, it doesn't really change, so we would say that there is no main effect happening with a.

02:49 So then we can look at b.

02:51 Now, like i said, the b lines, one's going up, one's going down, but they're pretty even in how much they go up and down.

02:58 They seem to kind of cancel each other out.

03:02 Now, if our lines will cancel each other out, then we do not have a main effect happen.

03:10 So that is all one example of just, you know, what you should look like if things are interacting and if there's no main effect for a or b...

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