 I'm just going to give you a definition of negative versus positive controls because we're going to look at types of controls through the whole course, but I want to give you a definition. And I'm going to give you this definition and acknowledge right up front that this is weird. The types of controls, first of all, why do we need a control? The control ensures that we have something to compare our results to that lets us draw a conclusion about the results. If all you do in our example with brain shrimp, if all you do is change salinity and you don't have any like predicted best outcome for or like the old I don't know where they live. Normally, I don't know if you don't have something where you're like, this is what I'm going to compare to. I know they live in this environment. What how salty can they get? If you don't have that thing to compare to then you don't know like did they all die because they always all die. Did they all die because it was salty? The control gives you something to compare to now two types of controls. We have a negative control and a positive control. And again, this is going to be the longest I hope this is the longest lecture we're going to have. That's probably really optimistic of me to say so please do not do not be afraid. This is a long lecture because this is a complex like we got to get into this stuff and it's complicated because you already have seen the process of science is all over the place and it's important that we have a good understanding. I'm going to give you a definition of a negative control and a positive control and then we're going to practice the whole semester identifying them so that you don't feel like just can't even visualize what this means. Negative control yields no results. So a negative control is going to be something you're going to expect to yield no results and I'm going to give you an example. A placebo is an example of a negative control. When you are, for example, studying a blood pressure medication. The treatment is the blood pressure medication. The negative control is a pill that looks just like the other one has the same mass as the other one, but is made entirely of sugar, something that should not impact your blood pressure. Does that make sense? So the negative control is going to yield no results. That way you know if the pill has similar results, the treatment has similar results to that negative control, you know that this means that pill doesn't work. We know what no results look like. This is interesting because there is a thing called the placebo effect in which like 30% of folks receiving the sugar pill will have positive blood pressure outcomes. We need to know that is that the placebo effect that is happening or is it the blood pressure meds that actually are having an impact. So if the blood pressure meds don't do better than 30%, then you know that here's what sugar does, nothing. And yet placebo effect indicates that we have some impact on this from the sugar pill. The blood pressure med itself is either going to have a bigger effect than the placebo effect. Or if it's about there, then we would know that, you know, there's probably a placebo effect here, but we don't know if there's actually something more. Does that make sense? I think it's, I don't think it's, there's something not intuitive about these controls. If a negative control yields no results, what's true about a positive control would you expect? A positive control is going to yield expected results. So in our blood pressure example, a positive control, the expected results would be treating the patients, a pile of patients, treating them with a known blood pressure, effective blood pressure med. Same size pill, same every, but we know it works. So let's see what would we expect to see if we had a known positive outcome. Then we can say, okay, we had 30% of the folks had their blood pressure impacted in the treatment group, 30% had their blood pressure impacted in the negative control, and 90% had their blood pressure impacted in the positive control. Therefore, we're going to conclude that this treatment was not effective. It was closer to the no results than to what we would hope for in good results. How's that? Those are our two types of controls. And again, we'll just keep messing with it and trying to identify the types of controls all the way through the course. Next up, we're going to look at an example experiment before wrapping it up with measurement and graphing.