Cohort and case control study

hi Venus I'm back here to discuss one more important topic related to your community dentistry has already discussed in the previous video about different types of study now I'm going to discuss two important studies which are most commonly asked for us that is cohort and case-control okay so it's very simple that most of you have did this at your best that the difference between cohort in the case control study is a star question for your final year university exams and you simply know that one goes in opposite direction like cohort is quite opposite to the case control in most of the situations and most of the conditions so it's better we learn one type of study and most of the things are opposite to other study so coming to the first aspect that is cohort study cohort study and the second aspect is the case control study so cohort study is a four word study for word study means simple I am going to give a simple example that okay a high-carbohydrate sticky foot a high-carbohydrate sticky foot on taking a high-carbohydrate for its sticky furred for a longer duration of time for a longer duration of time for example a five years or ten years which may lead to dental caries this is hypothesis which may lead to dental caries right this is the hypothesis means this study is moving forward so this is an example of a cohort study means you are watching a person or a group of people who are taking high carbohydrate sticky died every day our observation of five to ten years there is a dental caries occurrence similarly you can do this in Reverse direction okay you have selected a people who has dental caries who has dental caries who as dental caries and you've got the history from them about their dietary habits okay means you are going in the reverse direction that study is called as case control study cohort studies a forward study it is also called as prospect to study okay whereas case control study is called as a backward study okay proper spell to study mean study which is going backwards for example in most of your questions they will give you a study has started okay a study has started okay in the year 2020 and we are studying for the upcoming ten to fifteen years for example ten years the upcoming ten years that is 2013 means the dates simply shows that the study is moving in forward direction the study is moving in forward direction this is a cohort study similarly they are going to give a cases were taken disease cases were taken and their history was taken ten years back from a hospital or from any other source ten years back means if the dates are going in a backward direction then it is called as a case control study there is one exception something called as nested case control study that is called as nested case control study means nested case control study is nothing but a combination of cohort study as well as case control study okay simply nested case control study is a combination means is a combination of both is a combination of both means you know you are in 2020 okay for example you are talking about regenerative endodontics cases so already in a particular department in the last five years from 2015 to 2020 there were lots of region at 100 region a day two cases were done and similarly you are planning to do hundred more cases from 2020 to 2025 so this study is going in forward direction okay but you are collecting data in backward direction also so it is a combination of forward direction and a backward direction that is called as nested case control study okay that is called as nested case control studies the simple you can add a bird to nexted case control study as as a study as a study as a small case control study which is nested in a cohort study is a small case control study which is nested that is the reason why it is called like that which is nested in a cohort study so are they can simply ask nested control study is which type of study is a cohort study because it's moving forward it's mainly a cohort study but you are collecting data in the retro prospective direction also so it is a case control study nested case control study is is more often a cohort study the major aspect is quad study as it is moving forward but you are collecting some data previously also so it is a part of case control also mostly it is a cohort study but a part of case counter so don't get confused nested case control means most of us feel that it is a case control study no it's not a case control study it is majorly a cohort study with some amount of case control study I hope you're very clear so they can give us something like this some example like this so you have to go for a better option like nested case control study because a study which is moving both forward as well as backward is a nested case control study I hope you are very clear that nested case control study is most commonly used for diseases which are new or diseases which are rare or techniques which are new for example now in this particular example I am talking in regenerative endodontics which is a new technique or a condition in which the diagnosis is impossible or very expensive for example if you want to go for diagnosis of Pulp vitality in this case it is very difficult to analyze the pulp vitality in this case because we have very less equipment for that okay so when to be done for this study is the disease should be rare or new or the technique should be rare or new the diagnosis is impossible or expensive in such conditions you can do next or case control study hope you are very clear with this right so I'll be talking more about cohort study now and you can learn the quite opposite is the case control study so cohort study has already discussed is a forward moving study is a prospect to study okay so what prospect to in 2020 okay you have taken hundred cases and all these hundred cases are being exposed to the smoking predicting that by 2025 or by 2030 you are expecting parentage this is your hypothesis that smoking is a of occurrence of paradin titus and your study is moving forward direction this is your cohort study right I hope you are very clear with the cohort study they're few the main disadvantages because as it is taking five years time or ten years time as it is moving forward the main disadvantage of this cohort study is time consuming it is it consumes it is it is consuming most of your time okay and most of the things has already mentioned you're smoking the smoking here as we have taken as a theology or a risk factor you have some some keywords which are used in this particular study smoking can be called as a cause it can be called as a cause or smoking can be called as an exposure or the smoking in this particular can be called as a risk factor okay so if it is a risk factor based thing it is called as the outcome is called as effective means the periodontitis is called as an effective if it is exposure based things it is called as out compared to entities as outcome if it is a risk based thing the periodontitis is called as disease so the case control the cohort study cohort study can also be called as cause-and-effect to study can be called as exposure and outcome study can be called as risk factor and disease study can be called as any of these these are the other terms that are used for the cohort study and as already mentioned like what you are going to do in quod study in this particular case in 2020 you have taken hundred cases and they started smoking and you are going to identify the parado entities and out of which in 2021 you have identified two cases developing periodontitis in 2022 there were four cases which has developed in 2023 there were ten cases in 2020 for zero cases in two thousand I'm just giving an example twenty five there may be 50 cases developing periodontitis so every year there we you are checking number of cases the number of new cases so the number of new cases are what are the number of new cases in a particular duration of time called as incidence so this study is also called as incidence study okay it is called as cost-effective study it is called as exposure outcome study it is called as risk risk factor disease based study it is called as incidence study as you are getting the incidence and everything okay so what is the what is the aspect like you are just taking an explore you are just taking the normal person who is being exposed to the Carrey's sorry who is being exposed to the smoking and periodontitis okay similarly there may be other factors also leading to periodontitis smoking is one factor okay there may be other factors also so how you have to take this particular case in 2020 okay so there were few people who were exposed exposure and you have to take non exposure group also so you have to take hundred exposure group to smoking 100 non exposure group okay so by 2030 by 2030 eighty people have developed paradorn Titus who are smoking and and the second category there were only 10 people who are developing paradorians they are not smoking but they have periodontist that can be due to any other reason so this is an example that we are taking so you have to take two groups for a comparison one is the exposure group and second one is the non exposure group the exposure group here is the smoking the non exposure group can be any other factors so by taking this data if a particularly this data is given that is most often Li related to cohort study so with this data you have to get the strength of Association how to get the strength of association is they are three important parameters for getting the strength of Association in cohort study they are one is the relative risk the second one is the second one is the attributable risk the third one is the population attributable risk okay the three factors one is relative risk second one is attributed risk third one is population attributed is so these are the three things which helps in knowing the strength of Association the strength of association between the smoking and everything okay mostly the strength of association is obtained by relay to risk I hope you are very clear until this point okay so now you have to compare the other aspects okay what we are going to compare first we are going to talk about the really do risk okay so what is related risk simply okay relative risk is equal to you have to remember this formulas incidence among the exposure by incidence among the non exposure is a relative risk formula so if you take the relative risk formula for this particular case incidence among the exposure is 80 persons getting periodontitis out of 100 so incidence among the exposure is 80 by 100 and incidence among the non exposure is ten by ten by hundred so it is eight percentage so not person s it is eight okay the relative risk value is 8 so what this 8 means means the relative risk of smoking is 8 times more than an on exposure thing to cause periodontitis means smoking causes smokers causes eight times more prone or relative risk is 8 times more when compared with non-smokers okay so what relator is quali gives us relative risk well if it is greater than 1 it gives a positive association positive association relative risk value 0 1 gives equal to 1 use there is no association means you can conclude that smoking is not a relative risk factor for occurrence of periodontitis if related risk value is less than 1 then it is called as a negative association negative means it is a preventive measure means smoking is a preventive measure for occurrence of periodontitis okay so now the value is 8 means more one means smoking has an association with occurrence of Parador notice how many times 8 times occurrence that that is that is what the relative risk is going to give you so while you're done with the first one that is relative risk is over so we are going to the second one what is second one attributable risk AR right so we are done with relative risk now we are going to talk about attributable risk okay so what is okay so next one is attributed risk so you need to make a note about this formula attributable risk is equal to incidence among exposure - incidence among non exposure by incidence among the exposure in 200 make an or don't forget this hundred because this is a percentage okay so what is the incidence among exposure is eighty by hundred incidence among non exposure is ten by 100 by incidence among the exposure is 80 by hundred if you calculate this you will get a value of eighty eight percentage so what does this attributable risk gives an idea that smoking is an etiology the etiology of smoking is eighty eight percent test means the currents of occurrence of parado entities in the smoking people okay smoking people or the association of the association of smoking as an etiology is going to be eighty eight percent is is the inference that is given by the attributable risk so the last one is population attributable risk so the formula for population attributable risk is incidence among the total population - incidence among the non exposure by incidence among the total population so the total in two hundred okay the total population is 200 here so incidence among the total population is how many people are getting the this more periodontitis is ninety by how many people are there 200 right - non exposure is ten by hundred by 90 by 200 so this is going to be somewhere around 70 77 or 78 percent as if you calculated okay so this is going to give an idea if you prevent smoking if you prevent smoking there will be drop of 77 percentage of the cases okay so it's a preventive measurement which can be taken the entire population that if you prevent this particular factor the occurrence of smoking or the smoke the periodontist will be decreased by 77 percentage so these are the three important factors the number one is relative risk number two is a our number three is pierre so these are the three parameters which we are going to get with the help of a cohort study okay I hope you are very clear so other important things the the other names are forward-looking study prospect to study study which moves from cause to effect study which moves from risk factor to disease study which moves from exposure to outcome this is also called as incidence based study so all these things which we have discussed and they can ask you one more question the minimum number of cohorts that are required in cohort studies the minimum two because you need to compare like one exposure group one non exposure group the minimum number of cohorts that are required is - okay so you can ask me that how the relative risk or attributable risk or peer how where they are used or how they are used for a normal thing okay so relative risk is most commonly used by the clinician by the by the clinician normal physician will will take this relative risk into consideration and we'll explain the patient that if you do smoking the risk of getting the risk of smoking for periodontitis will be 8 times so this is how a clinician will use relative risk most oftenly next attributable risk is most commonly used by epidemiologist ok innovative risk will be used by this particular individual when he collects a data whereas the Pierre is something related to enter population which is used by Public Health Program Manager this person is going to use that okay this factor is how much influencing the occurrence of paradorn Tidus in a smoker so in a smoking population okay I hope you were you were clear with concepts what we have learned related to this so now we are going to solve few important MCQs okay the study of smoking for 10 years and occurrence of periodontitis is similar example what we are discussed so you are you are planning to study the effect of smoking to occur the para donar this means it is simply going in a forward direction you are not collecting any information the answer is cohort study how it can be a case control studies you have selected the smokers okay a hundred smokers were selected hundred smokers were selected and their case history about the smoking in the last five years was collected means then you are going in a reverse direction then it's going to be case control study the second one calculate the relative risk calculate the rate of risk in which the incidence of the disease among the exposure is twenty and non exposure is four okay so exposure incidences given us twenty incidence among the non exposure is given as four so they're asking to calculate the relative risk we have learned the formal of relative risk that related to risk is a ratio between the incidence among the exposure by incidence among the non exposure so incidence among the exposure is twenty non exposure is four so the relative risk is okay the relative risk valley is i hope you are clear with this the next one attributable risk is measured by so we have learned that there were three association that we are measuring one is relative risk second one is attributable risk third one is population attributable so all these are measured in cohort study so attributable risk is measured in cohort study max activatable this gives a brief idea but we have already learned the related risk is going to give how many times that this particular cause is a risk factor for causing a disease a typical risk will talk about the etiology that for a particularly theology which is which is causing this disease in a particular group of individual this percentage so we have already learn about this so this talks more about the etiology factor or a factor in the disease right so thank you for now signing off dr. shreek on from team MDS conquer so we have we have done different studies and we have almost completed the case control study and cohort study okay so I hope you can manage which I mean when they gave a description of a particular study you can even clearly identify that would study this is and of course you now you can calculate the relative risk attributable risk and the population attributable risk and you have learned some important advantages and the disadvantages and of course please do try to finish that the difference between the cohort study and case control study which is there either in your shobun pater or parkour or the Vivek chain of a change social medicine I'm sick you poke any of these beautifully given so all the differences has to be you need to make a note because most of your questions will move around case controls and cohort study for sure