Negative & Positive Controls

by Jason Amores Sumpter
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in this video, we're going to talk about how scientists avoid or prevent false positives and false negatives in their experiments by using negative and positive controls. And so really, there are two main types of controls that air used in experiments once again, the negative control and the positive control. And so, ideally, these control groups are on Lee going to differ from the experimental group in the one factor that's being tested. And so notice down below. In this little table here, we're going to distinguish between the two types of control the negative control and the positive control. And so, in the first column here, what we have is the control type, which once again are gonna be the negative control and the positive control. Now, the negative control, as its name implies with the negative here. By definition, it's gonna be the control group where no response is expected. And so it's expected to react negatively to the test. And that's why it's called the Negative Control. And so, for example, this would be like using something like a placebo, which is like, Ah, fake pill that's not supposed to do anything at all like a sugar pill, for instance. It shouldn't help with healing any kind of injury. Now the purpose of using a negative control would be to prevent false positives, which we defined what false positives are in our last lesson video. Now the positive control, on the other hand, by definition, as its name implies, is going to be the control group where a response is expected. So it's supposed to react positively to the test, and that's why it's called the Positive Control. And this would be, for example, using something like a brand name pill that has been proven to work successfully in the past. Now the purpose of using a positive control would be to prevent false negatives. So if we take a look at this image down below, what we have is an example of an experiment where they're testing this brand new experimental pill to see its drug effectiveness on the toe injury here. Now, if we are testing this experimental pill, that's brand new on how well it's drug effectiveness is on healing this toe injury. We might want to include a negative control group and a positive control group. Now the negative control group would be something where we have expectations that it will not react. There will be no response. And so, for instance, using something like a sugar pill would be an example of using a placebo, something that is a fake pill and is not supposed to do anything. So if you eat a sugar pill like this one right here, it's not supposed to help heal your toe injury. And so because we have expectations that the sugar pill is going to react negatively and we'll have very, very little drug response Uh, that is the negative control. Now, over here, what we have is the positive control on the positive control. We have expectations that it will react positively, positively. It will show a response. And so, using something like a brand name pill that has been proven to be successful with helping with toe injuries would be an example of a positive control, because once again we have expectations that it should react positively and it should have some level of drug effectiveness. Now notice. Over here on the right hand side, what we have is a graph. Where on the X axis over here. What we have is the independent variables which the scientists have control over on that is going to be the exact type of pill that they decide to use. And then on the y axis of this graph, what we have is the dependent variable, which is what the scientists are going to measure, which would be the drug effectiveness and how good it is at healing the toe injuries. Now, once again, the sugar pill here is going to be our negative control because we have expectations that it should react negatively. So it should not help with the toe injury at all. And it should be 0% drug effectiveness. This is what it should be now. If we were to actually use this sugar pill on a group and it was to show that it had, ah 100% drug effectiveness, then this would be an example of a false positive. And so, by including a sugar pill, a negative control group, and having this negative control group respond, as is expected, that is helping to prevent false positives. Now, on the other hand, over here, what we have is the brand name pill, which we said is gonna be the positive control here because we have expectations that it should react positively and it should give some level of response, maybe not 100%. But it should give some level because in the past it's been proven toe work successfully on helping toe pain. And so once again we would expect some level of drug effectiveness. Let's just say somewhere around here, and so that's the expectation Now, if this brand named Pill were to somehow have 0% drug effectiveness, then that would be an example of a false negative. And so, by including the brand named Pill here and having it respond as expected, we're helping to prevent false negatives in our test. And that's exactly what we said here, where the purpose of the negative control to prevent false positives and the positive control to prevent false negatives. Now the experimental group here would be the brand new experimental pill that we're testing for maybe the first time. And so this experimental pill might respond, Uh, in any level, it could respond anywhere from here all the way up to 100% now if it responded below the experimental. I'm sorry if it responded below the brand name pill. If it had less drug effectiveness, then maybe the scientists would be like, Hey, don't use the experimental pill. It's not as good as the brand name pill. But if the experimental pill responded better with better drug effectiveness, then maybe the scientists would say, Hey, try this experimental pill because it might help with your toe pain better than the brand name pill over here. And so you can see here how positive and negative controls can be very, very helpful and very useful for a scientist. And so this year concludes our introduction to the difference between negative and positive controls, and we'll be able to get some practice moving forward and our course, so I'll see you guys in our next video.