 Let's continue on and discuss some behavioral sciences. Specifically, we're going to discuss some studies. And we're going to compare and contrast six various types of studies. On this slide here, you'll see the cross-sectional study, cohort study, and case control study. The design of a cross-sectional study asks what is happening. This is going to look at the frequency of the disease and the frequency of the related factors or the risk factors that are associated at that specific point in time. This is like taking a steak and cutting it in half and seeing how the doneness of that steak is at that particular point in the steak. It might be different at various points, but at that one specific spot, this is what is happening. Cross-sectional studies measure prevalence. They can show a risk factor in relation with the disease, but they don't establish causality. A cohort study asks what caused the disease. This compares groups with given risk factors and given exposures to groups that don't have those exposures or those risk factors. So we can see in a cohort study if having a risk factor increases our risk of having this disease. It's associated with a later development. Is it associated with any development? These can be prospective, meaning we look ahead into the future or it can be retrospective, meaning at this point in time a patient has a disease and let's look back and see in their history do they have any exposure to a certain chemical or carcinogen or product or environment. Cohort studies will measure relative risk. So you can kind of remember that as the RT in cohort is translated into relative risk. So the R in relative and the T in relative. Case control studies ask what happened. This looks at disease groups and it compares it to a non-diseased group. What happens is there a risk factor that differs by the disease state. So seeing this group over here that has COPD, did they have a risk factor of smoking in the past compared to those other patients that don't have COPD? Do they have a risk factor of smoking in the past? As you see on this last line, the odds of prior exposure based on current disease. And this measures odds ratio. The three final types of studies we'll discuss are crossover studies, twin concordant studies, and adoption studies. This is comparing the effect of more than two treatments or two or more treatments on a participant. So patients will receive one treatment and then they will change to a different treatment and see which one helps them better. There is a period of time in the middle of that where there's a washout where they get rid of a medication and allow the body to process it out before we start another medication. One way to help with bias on this particular study design is we do randomize the order in which they receive these treatments. So one patient that's in the study might receive treatment A while the other patient receives treatment B and then they swap halfway through. Crossover studies have a strength in that they allow participants to serve as their own controls. So taking a medication might be a placebo and then taking the actual medication shows us what is the actual effect of this particular medication versus not having a true medication or is taking medication A that might be this current standard of care better or worse than taking medication B that could be a new medication. The twin concordant study compares the frequency with which a disease develops amongst monozygotic twins versus dizygotic twins. This is going to measure the various effects of nurture versus nature. This also measures heritability and an influence of the environmental factors. Finally, our last type of study that we'll discuss is adoption studies. This is going to compare siblings that are raised by biological parents versus adoptive parents. It is going to measure heritability and an influence of environmental factors. Do siblings that have similar genetic makeups do better in one type of environment or another? Is there anything that influences them in one direction or another?