So let's discuss the case series first. Now this is really the simplest form of research you can do. And depending on the setting we have other terms for it. We call it a clinical series, or even an audit. We just want to find out how many of the certain type of cases we are seeing. You might ask yourself, when it's so simple, why do we do it? Well, it can really help us identify problems that we might be dealing with. Or areas of interest, or areas of concern, and it can really help us plan our further research. Now I want you to consider an example. This is by Donald and his colleagues from the nearby Red Cross War Memorial Children's Hospital and from the HIV encephalopathy clinic. Now it's a very common neurological disorder in these unfortunate children. And all they wanted to do is just describe this set of children, identify challenges they might be facing or their parents might be faced with, and any opportunities to improve their lives. So they went to the clinic, and they chose 87 children form this neurological complications HIV clinic and they worked from a pre-designed forms containing many variables. If you look at the data that they collected really the age, the gender, the birth history, were they premature, type of labor, was there any early developmental problems, when did they start walking, was there delay when they started walking laboratory counts like cd4 counts, viral loads, etc. So all sorts of data is collected on these 87 children. And if you look at the results section, all they did was describe those data points that they had, the variable they looked at under the background info they described. What the gender was, how many were males, how many were females? What were their ages? When did they start on Antiretroviral therapy? What was their home environment like, their school environment? That they had been the repeating of their grades, etc. They just described this subset of children. They describe the clinical information you can read all about the immunological status. What was this CD4 count? What was their viral load? Some of them had imaging, MRI and CT scan. And they just describe the findings. It might sound very simple. They just had one group of patients for the most part of this study and they just describe those children. But I want to read a quote from the study for you just to really bring home how important this type of study can be. And they say, the school failure is a major problem in this group and in society where HIV remains highly stigmatizing and the school is frequently not aware of the children's diagnosis, many parents are reluctant to seek help for their child's learning problems. So, we can describe that one group of children and we can come up with so many problems that they face here, and we can now design ways to help them and ways to do further research to answer many more questions surrounding this. So, case series remains a very important study design in the literature.