[SOUND] >> [MUSIC] >> Welcome. In this module we're going to discuss different types of epidemiologic study designs. These include both experimental study designs and ob, observational study designs. Sometimes we need to use observational study designs because there's some types of exposures that cannot be randomized, it's not ethical. So we'll learn both about experimental and observational study designs. [MUSIC] In this segment, we will introduce you to experimental study designs. We are going to cover several different types of experimental study designs, both randomized control trials, and case crossover studies. After you have reviewed this lecture, you should be able to complete these learning objectives. They include: describe the differences between experimental and non-experimental or observational study designs. List two different units of analysis, explain the purpose of randomization. Characterize randomized control trials and clinical cross over study designs. Identify the advantages and disadvantages of randomized control trials. And define the following terms, blinding, equipoise, placebo and intention-to-treat. If you learn about different study designs and their advantages and disadvantages, you're in a better position to interpret and evaluate the results from various research designs. The most important distinction of an experimental study design compared with a non-experimental or observational study design is the exposure assignment. One example of this would be randomizing one group of patients to get the new breast cancer chemotherapy drug and the other group of patients to receive the current standard chemotherapy drug. Recall that exposure is the intervention. For example, a new drug treatment. And in the experimental study the investigator usually determines who is exposed and who is not exposed. The exposure or intervention is randomly allocated to study participants. To test if bed nets reduced infants contracting and dying from malaria researchers randomized a group of infants to receive bed nets from birth onward. The control group of infants received bed nets after six months. Researchers found that the use of the bed nets in infants reduced the rate of both developing malaria and dying from malaria. In a non-experimental or observational study, the investigator does not assign exposure status. For example in an observational study on the health effects of living near nuclear reactors such as Fukushima. The investigator does not assign some people to live near the nuclear reactor and others to live far away from the reactor. Another example of a non-experimental study would be to follow a group of diabetes patients over time. Some of whom smoke tobacco and some who don't. And then look at what their rate of cardiovascular disease is. Examples of experimental study types include randomized control trials. We will be discussing this in greater detail in this video. Examples of some non-experimental or observational study designs are case-control, cohort, ecologic and cross-sectional studies. You will learn more about these designs in other segments in this MOOC. An important difference between experimental and non-experimental studies is the randomly assigned exposure. Randomization is important because it minimizes differences in key characteristics between the group that gets the exposure and the group that does not get the exposure. But it's not ethical to randomly expose people to serious hazards such as radiation, toxic chemicals or inadequate health care. Therefore, experimental studies designs don't work for everything. Instead, researchers use observational studies in these situations. In experimental studies sub, study subjects are assigned by a formal, usually chance mechanism between two or more exposures or interventions. Experimental studies are the gold standard for inferring causality. Commonly, experimental studies provide participants with an exposure, such as a drug, that may be either therapeutic or preventative. The provided intervention is usually randomly allocated but not always to study subjects by the researcher. Next we will cover two types of experimental studies, randomized control trials and clinical crossover trials. In a randomized control trial, the treatment of interest, such as a new drug, would be randomly allocated to half of the study subjects. And the other half would receive a placebo or the current standard of care or medication for the disease. An example of a randomized control trial would be a study comparing two different treatments for arthritis. Subjects would be randomized to one of the two arthritis treatments. In a clinical crossovers trial, subjects switch from one treatment to another after a certain period of time. They, quote/unquote, crossover to the other treatment or exposure. We'll go into more depth on this type of study later in this module. Experimental studies commonly provide participants with exposure such as a drug that may be therapeutic or preventative as I said earlier. There are both individual and community experimental studies. And example of an individual experimental study is where one group receives an experimental drug aimed at preventing Alzheimer's disease in an at risk group while another at risk group receives a placebo drug. Experimental studies can also be targeted to communities rather than to individuals. An example of a community intervention study is a colon cancer screening program that was implemented in nine counties and seven control counties who did not receive the screening program. So this relates to unit of analysis. Let's talk about unit of analyses in these studies. Let's remember that there are individual and community-level experimental studies. In an individual-level experimental study some study participants are assigned an exposure. And the remaining participants are assigned to be unexposed or exposed to a different factor. In a community level experimental study one or more communities is assigned to an exposure. And one or more other communities are assigned to be unexposed, or exposed to a different factor. Thus the unit of analysis for an individual experimental study is the individual, whereas for the community level study the unit of analysis is the community.
