 Good morning everyone let's continue our epidemiology session. So today we will be seeing the descriptive epidemiology. So I was talking about epidemiological basic study designs that is observational and experimental. So in observational we had descriptive and analytical epidemiology. So today we will be seeing in detail about descriptive epidemiology. So descriptive epidemiology we had seen many study design one was case report case series longitudinal study and cross-sectional studies. So how to conduct a descriptive epidemiological study. So this is a very common study which everyone can easily perform and it is a very first step of any type of study. This is just a collecting data collecting data of any group of people regarding any particular disease or anything. So that is all about descriptive epidemiology in short. So we can say that this is a first phase of epidemiological study. So we will be observing the distribution of disease how it is distributed among the people and what are the characteristics of the disease associated. So these are the common things which we will be doing in descriptive epidemiology. So all these things you can see the example of a descriptive data this is number of death per person and by one lakh people one lakh live birth. So you can see that the death is going on decreasing as time goes forward. So this is 1936 and this is 1975. So the number of death is decreasing over a period of this is sorry not 1975 this is 1750 to 1975. So this is the data of the child death in among one lakh live births. So this is an example of descriptive data. Similarly the death rates of heart disease over in six countries. So these are the death rates which is showing in these dotted line graphs. So these are the death rate in the y-axis and the year in x-axis. So it is just giving a data of death rate in various countries during this period 1952 to 2010. So what are the basic steps in descriptive epidemiology. These are the fundamental steps. So the first is defining the population. So suppose we have a problem in front. So we are going to conduct a study in a population. So we need to define the population. Okay. So the second one is defining the disease under study and the third one is describing the disease by using time, person and place. The fourth step is measuring the disease and the fifth step is comparing with non-endesis and finally the ultimate aim of descriptive study is to formulate hypothesis. So we will come in detail by each step. The first one is defining the population. So we go to a population which includes lot of people, various gender, various socioeconomic status, various occupation, various classes. So we need to define our population to be studied. Suppose the same example we took, we take x-ray, we have taken an example of cholera. So we need to constrict our population to a group of people who might have had consumed water, the suspected water because water consumption might have caused this cholera disease. So in a particular period of time, people who have had consumed water from a particular hotel or a particular common tap must be our population. We cannot just take the entire population because the population will be very huge. So we need to constrict and we need to clearly define our population where we are going to conduct our study. So that is our population defining. Otherwise the study which we are planning to conduct will be very difficult because the population will be too huge. It will take up majority of our time, expenditure and will end up with nothing. So if not to get a good result, we need to define our population exactly which group of people we want to conduct the study. So you can take the example as cholera disease. People who have consumed water, suspected water from the particular source should be your population. So the next is suppose you can take an example, the same example you can take. This could be the total population in that town or society wherever it is. So the target population will be too huge. So you cannot include all the people in that population. You have to take a small sample of the population. When we define our population, the population will be little more big. Still it will be as big as the study is not possible. So we need to take a sample from the population. So this will be our target population. People who have had consumed water from the suspected source. So we may not be able to take entire the target population. Target population is a total population who might have had drank that particular water from that particular source. There will be many people, there will be thousands of people. So we cannot take the entire population. So what we do is we take a sample out of it. It should be representative. So the second step is the first step was defining the population. The second step is defining the disease and the study. So population already defined. So next thing is to define the disease and the study. So the cholera disease or any disease which need to be clearly defined. So what happens is we need to keep an operational definition. Not the exact definition. We need to keep an operational definition and give you an example. Tonsilitis is a disease. So our operational definition will be, see the normal definition is like inflammation of the tonsils caused by infection usually with streptococcus pyogens. But we will convert it into the presence of large red tonsils with white x-ray which on trot sap culture that has predominantly streptococcus pyogens. So our operational definition is this. So our cases will be only persons which follows or which actually have this operation definition rather than this definition. So this is a WHO definition or a clinical definition. So we will convert the clinical definition into operational definition and we follow the operational definition for all the patients. Only the patients which has operational definition criteria will be considered as case. Otherwise they will not be considered as case. Why we are doing this operation definition is to restrict the people. Restrict the entry of people. Otherwise we might get a lot of people which will be very difficult to incorporate into this study because epidemiological study is always limited to a smaller sample here because larger studies are not possible because of many factors. So we need to control our population size but at the same time we need to make sure that the population is representative and the sample should represent of that population. So that's why we are defining our population and we are defining our study so that the population size can be restricted without losing the quality of population. So the sample will be having the sample will be having the same properties of the population. It is supposed to have the same properties of population. So those two steps of one is the defining our population and the second one is defining the disease. So operation definition we keep. In cholera it will be a different operation definition. I have just kept this translate is for easy understanding. So once we define our study it is easy to categorize the patients as disease or non-diseased. If we keep clinical definition we make it a lot of patients. Some of them might not be useful for our objective or our particular study. So operation definition is always important in any epidemiological study that is descriptive study. The next part is the most crucial part of our descriptive study that is the describing the disease. We need to describe the disease under three headings that is time, place, that is time, place and person. So we need to describe the disease. So if we say it is time we commonly ask these three questions that is time distribution. When is the disease occurring? So if we go to the cholera example we ask the people when was it happened, when is it occurring and where is it occurring and who is getting the disease. These three things we need to find out. The time, place and persons, when, where and who. These three are the most important thing in descriptive study. So time distribution we may go into detail. So we need to find out how the usually diseases are getting classified under short term fluctuation, period fluctuation, long term or secular trends. The diseases are very different in its output. How they present, how they show symptoms in people are very different. So patterns of diseases are different. So time distribution we know short term fluctuation. If it is epidemic it will come suddenly a lot of cases appear overnight in a two, three days of period and it will go just like that. So that is epidemic, occurrence of more number of cases that is excess number of cases that is epidemic. But this is very short term fluctuation. We know common cold influence short term fluctuation which is having very shorter duration. So types of one will go through a little bit about the short term fluctuation or the epidemics that is common source epidemic and the propagated epidemic we know person to person the corona is spreading from person to person from other port from annual reservoir. If it is based on the source point source per a single person is spreading the disease or continuous or multiple exposure or slow epidemic. This is just a sub part of this class that is types of epidemics. So under short term fluctuation or under time distribution we are seeing short term fluctuation and in short term fluctuation it is commonly epidemic and we are seeing just examples of some of the epidemics. Epidemics can be classified as common source propagated and slow epidemics. We will not go into much detail point source means a single person is giving a lot of disease or a point source is giving a lot of cases that is Bhopal case tragedy or a foot poisoning. Common source common sources will have contaminated water or a prostitute infected with gonorrhea. So this is a common source which spreads repeated exposure but before I was talking about single exposure. So single exposure is a single place or a single locality which is spreading a lot of diseases not a single person. So it is like foot poisoning and Bhopal case tragedy and here it comes a common source there we have a prostitute infected with gonorrhea or a well of contaminated water where a single source or a common source is spreading diseases and propagated epidemics with seasonal trends and cyclic trends. So seasonal trend is we know measles usually occurs in early spring and respiratory disease which we commonly see in winter and GIT which commonly seen in summer this is a seasonal trend. Whereas in cyclic trend we know before the vaccination era measles used to happen every 2 to 3 years. Roblo every 6 to 9 years and influenza every 7 to 10 years. After the vaccination period these all are not very common. So automobile accidents are more frequent on weekends that is Saturdays and Sundays. It is a cyclic trend before we study seasonal trend that is upper respiratory tract which is common in winter and measles in early spring. And long term or secular trend is like common heart disease or lung cancer, diabetes which is very common in developed countries but now India and other developing countries are also becoming cases are increasing but usually it happens over a very longer period. So secular trends or long term trends it is like commonly seen these type of diseases in the western countries. And now it is slowly slowly changing and a big shift will happen in a very longer period of time. So what we have seen is epidemics. The type of epidemics it was under time distribution, short term fluctuation and epidemics the types of epidemics like common source, propagated and slow epidemic, under common source the Bhopal gas tragedy and food poisoning and continuous or repeated exposure that is prostitute of gonorrhea and well of contaminated water and propagated epidemics and periodic fluctuation. So before we were seeing short term fluctuation now we are seeing periodic fluctuation just a little bit messy it comes in between the descriptive epidemiology but anyway epidemic is a commonly asked question so you need to know in detail about epidemic. So seasonal trends, periodic fluctuation we have seasonal trend and cyclic trend, seasonal trend we talked about missiles and respiratory diseases, cyclic trends, pre-vaccination and vaccination era and automobile accidents, long term trends, the cancer we have seen in the developed countries. So we have covered the time distribution now the place okay so place we need to find out where all it is happened that this is how it is distributed in a geographical area. So what we need to find out if it is a big disease or if it is a pandemic or a disease which happened in a town state or a district or a country we need to find out the local distribution, the urban, rural differences, national and international variations okay. So international variations we were saying that cancer is very common in cancer of stomach which is common in Japan not in the US. So the oral cancers are common in India compared to western countries. So these are a place distribution international variation. So national variations we know some areas are endemic diseases which are like fluorosis, coveter, malaria, nutrition deficiency which are very prevalent in certain parts of our country. This is not very prevalent all over the country but it is some parts of the country malaria, fluorosis, endemic, fluorosis here in Kerala which is in Aleppo and Palakkad. So rural urban variations certain diseases are very common in rural sector like periodontal disease and certain diseases like dental keres is common in urban setup and the disease like bronchitis accidents, lung cancer, cardiovascular which is common in urban than the rural but whereas the zoonotic and skin diseases which are common in rural setup. So there will be variations for the disease according to the place rural urban the national variation international variations and local distributions. Local distribution how the disease is locally distributed. So this is one of the famous example how the epidemiology has come into existence. It is done by John Snow is known as father of epidemiology. So this was the case in Kerala. So this pump A was spreading the disease. So after he did a sport map he found out that the many casualties are around the pump A. So in local distribution you can do a sport map and sport the casualties or the cases happened. So you will get to know that it might be concentrated around some point that might be the point which caused the disease. So in this case it was a London happened in 1840s in London Broad Street Church a pump was there which is just contaminated Broad Street which was contaminated with sewage supply and it was producing a lot of cholera patients. So he accidentally found on that the pump was the reason and later the pump was changed and the disease abruptly stopped. So this was an invention or this was a discovery by the great epidemiologist John Snow and that's why it's known as father of epidemiology. So this is a sport map this looks like a town map where these black dots are the casualties due to that particular disease. So if we do a sport map in a very small area we'll get to know the we'll get to know a better picture of the disease. So this was all about place. So we have seen time and place the next one is person distribution. So how widely it is distributed within different accordingly like age sex occupation marital status habits and social class. So we collect data from persons and we categorize into age gender occupation marital status. So we can easily understand in which age group in which gender which social class which marital class it is distributed. So usually missiles happen in childhood, cancer in middle age and atherosclerosis in old age. So these are the few diseases which is very prevalent in certain age groups and gender few diseases are prevalent in males and few are in females and in occupation related diseases. Workers in coal mines usually have silicosis. These all are examples when we do a study we need to find out where it is actually prevalent. These are examples which I was talking about and social class few diseases are very common in upper class few are very common rural class I mean not rural areas that is low socio-economic background. We have reached the four steps. So first was the defining the population then defining the case that was describing the disease based on time place and person. In time we had fluctuation short-term periodic fluctuation and long-term trends and we had seen epidemics and time place and person. So the fourth step is measuring the disease. So we need to measure the disease by using any of our tools. So tools are like the measurement of epidermal she will be done by epidermal cycle tools that are rate ratio rate ratio and proportion. So we need to understand the amount of disease we need to quantify the amount of disease by using rate ratio and proportion. So the tools of epidermal she will be explaining another class. So we need to measure the disease based on these tools of epidermal she. So usually we calculate the incidence and prevalence incidence is the new cases and prevalence is the total cases. So prevalence means how much percentage of the people are affected by that disease and incidence is how fast it is spreading. So in epidemic we need to find out the incidence in a chronic diseases like cancer heart disease we need to find out the prevalence. So incidence is very vital in controlling an epidemic. So usually incidence can be found out in longitudinal studies prevalence can be found out in cross-section study. The fifth step is comparing with non-intensives. Once you get the data we need to compare with other population where the same problem has happened. We need to compare with other population and subgroups of the same population. So ultimately we get an idea of the disease etiology. Okay once we get the idea of disease etiology why after comparing this we need to do the hypothesis. This is the last step of descriptive epidemiology formulation of hypothesis. Hypothesis is nothing but an assumption after arriving from the observation after arriving from the collected data. So once you collected data you arrive at a formulation of hypothesis. So hypothesis is assumption about the particular problem. So drinking water from that particular pipe or drinking water from that particular restaurant could be the course of cholera. So we cannot say that it is a course you should say it could be the course. And in the next study design that is an analytical study we are going to test the hypothesis whether it is true or false and reject the hypothesis. That is the second step. So we have come to the steps. Okay so I will just recap it. The first step was defining the population. Defining the population. We have defined population and the disease operational definition we are given and describing the disease based on time place person and measuring the disease by using tools of epidemiology incidents and problems compared with other groups of same problem and formulation of hypothesis. So a little bit tricky part is the operation definition. We need to change the clinical definition to operational definition. I will come into the third step. You have time place and person. In time we will be studying more about epidemics that is comes under short term fluctuation. So epidemic is sudden increase in number. So common source propagated epidemic and slow epidemic. Common source has again a different division that is single exposure and continuous exposure. Single exposure is vocal gas tragedy continuous exposure is well of contaminated water and propagated epidemics which is person to person transmission and the periodic fluctuation we have seasonal trends and cyclic trends and long term of cyclic trends is another thing. The second part of the third step is place distribution describing the disease and the place. So there will be various variation international national rural urban and local and the third part of third step that is describing the disease under person based on age, sex, occupation, manager status and etc. So the fourth step is measuring the disease based on the tools of epidemiology. Commonly we use incidents and problems and the fifth step is comparing with non-intenses. We should compare it with different populations and groups and finally we arrive at a hypothesis that is a proposition or a supposition or an assumption about the cause and outcome. So this could be the cause for this disease this could be the that cholera could be the due to drinking water from that particular pipe or from a restaurant that is our hypothesis. So yesterday we had seen types of epidemiological study just to recap case report case series cross sectional and longitudinal studies. So case report is just explaining a case whereas case series it's like compilation of case report which happened at different time and different place so the same problem will be repeatedly mentioned from different parts of the world. So that is case series. In cross sectional study the population will be taken only at one point of time so this is a cross sectional study relationship of stress and dental caries and the students in bankluriosity. So these students will be asked about stress and their dental caries only one point of time okay. So longitudinal studies the same population will be checked at frequent interval of time or there will be a follow-up. For an example the health complaints after a malhotris chemical explosion a longitudinal study here you can see that the survey for 18 months which was started in 2008 and to 2012. So in cross sectional studies it was just like study will be done and study will be done either in 2008 or 2012 there will not be any follow-up in cross sectional study. Again you can see that association between developmental condition and microbiota and women during pregnancy longitudinal study. So there also there will be definitely a follow-up. So in cross sectional study sample will be surveyed only at one point of time whereas in longitudinal study t1 t2 the same sample will be time 1 and time 2 there will be time 3 4 there will be follow-up in longitudinal study okay. So that's all about descriptive study I have explained in detail about descriptive study. So the next class will be dealing with the analytical study okay. Thank you.