Get my FREE cheat sheets for Public Health, Epidemiology, Research Methods and Statistics (including transcripts of these lessons) here: www.learnmore365.com/courses/public-health-epidemiology-research-methods-and-statistics-resource-library
Thanks a lot, Sir. you made it so easy. It is so annoying that I have paid tuition fees for university and I still have to turn UA-cam upside down to understand every concept better.
At school you are given all the information you need to pass the exam. University is next level learning. At the university level you 'read' for a degree. It means that you are given enough information to go on, then you are expected as an adult, to read around your topic independently to develop your own learning skills, which are critical life skills that you will use forever more. UA-cam is an excellent place to find extra information and Greg's site is a nice resource.
+Kahtan Thanks for the question. So Retrospective cohort studies can be a little confusing because, as you mentioned cohort studies are usually prospective. The important thing to remember is that a cohort study is always looking at a group (a cohort) who have all been exposed to an identifiable exposure and we're still wanting to know if over time, what outcomes might be associated with that exposure. In the case of a retrospective cohort study, the timeline that we follow is in the past (and we have some record of who was exposed to what and what the respective outcomes were).
Hi Greg - In Kenneth J. Rothman's textbook; "Epidemiology: An Introduction (2nd edition)", Rothman talks about "Retrospective Cohort studies" (P.85). What is your take on that? He refers to a study conducted by Morrison et al. A study on data since 15th and 16th century in Florence. It is quite confusing (not what I needed on top of the heap of other epidemiology confusion) :P
Hi Greg. I am confused between retrospective cohort studies and case control studies. It seems like in both situations you look at people with a disease and people without a disease and then look back at exposure? Could you please explain the difference?
Can you give us an example for sake of deeper understanding when would you choose retrospective cohort and when would you choose case-control and under which circumstence would you choose one over other for a given problem?
Hi there - if you are looking at a rare condition - lets say hypothetically, people whose hair turned blue - you might want to consider a range of possible exposures that could have caused this. You'd look at diet, exposure to sunshine, genetics, the type of shampoo that they use etc. etc. (that would be a case control study). Start with the cases and look back at possible exposures. In a retrospective cohort (as in with any other cohort) your starting point is an exposure (not an outcome). You might for example be interested in what diseases have emerged following exposure to the radiation in Japan. There might be any number of outcomes. Your cohort is the group of people exposed. In this case however, the exposure is in the past (making it retrospective). Does that make sense?
Yes i finally think i do get it . If we have a known diesese but haven't figured out the causes yet, we will go with case-control, but if we have a known cause but we yet have to proove which diesese it can cause we will go with retrospective cohort.
Could you do a video on Attributable Risk, Absolute Risk Reduction (ARR), Number Needed to Treat (NNT), and Number Needed to Harm (NNH). These topics are all very similar and get confused. THANKS FOR YOUR VIDEOS!
ok, so in case case control, we already have the outcome and we want to find out what exposures lead to the outcome. so this study does access temporality right
thank you so much for this video it helped me in my homework for the epidemiology class.. you provided the information in a very easy and interesting way!!
Thanks for letting me know Marjorie Simpson (much appreciated). What are you students studying (and where)? Please let them know that they are welcome to get in touch with me if they have suggestions re future video content on this channel. I also host a weekly "live" global health news roundup every Wednesday at 2pm (EST) which that might be interested in. Find out more at www.twigh.org
Please can you explain the difference between a retrospective cohort study and case control study? I want to study exposure on an outcome of interest. For e.g I want to use health data and examine whether use of drug A prevents hospital admissions for group of infectious disease.
+MsZa124 Thanks for the question - it can be confusing. Regarding a cohort study - don't worry about whether or not its prospective or retrospective, the principle remains the same... you are looking at a range of possible outcomes in a defined groups (a cohort). That group is sometimes defined by a particular exposure (like whether or not they took Drug A - to use your example). Individuals in the group (cohort) may or may not become ill, or have some other outcome of interest. By contrast, in a case control study, your starting point is a group of people who are "cases" (who definitely DO have the outcome of interest). By comparing them to the controls you can establish whether or not there was a significant difference in their relative exposure to a number of risk factors. To answer your question, I guess it comes down to this: are you looking at just one drug with multiple possible outcomes (in which case you want to do a retrospective cohort study) or are you looking at a particular outcome (whether or not the person got an infectious disease) and you want to consider multiple possible exposures (in which case you want to do a case control study). It can be confusing. I hope this helps.
+MsZa124 I always say that the difference between a retrospective cohort and a case-control study is your defined baseline. In a case-control, you are looking today at a sample of diseased and non-diseased individuals, and asking them to recall exposures in their past (retrospective). In a retrospective cohort, you are also going back in time, but to a defined baseline point in time that happened in the past (e.g., all births in 2003). You will then follow your defined baseline point of time forward in time (e.g., 2003-2013) via records and secondary data to examine the difference in risk/outcome onset by exposure status. Hope that helps!
Dear Greg, thank you for this educational video. I have a quick question: how long would you recon a cohort study should last? If you write a thesis in about a year is it realistic? Or should it last over a number of years/decades?
Thanks for the question. The truth is that it's kinda like a piece of string... It's as long as it needs to be. That is to say, it depends on what's you're wanting to observe in your cohort. You may be looking at outcomes that take years to present (like cancer) or days (like the common cold). Hope that helps.
Hello! I have a question. Can you explain, why prospective cohort is not good for rare diseases and retrospective cohort is not good for very rare diseases? I know for rare outcomes, we should conduct case control studies. But what if, the outcome is rare but we do not have any historical data to conduct a case control study. Then in a hypothetical situation where funding is not a problem, what approach should we take?
Hi Ahmed - its a great question. On the whole, a cohort study is considered better than a case control study but it is sometimes not practical. So for example, if you are wanting to look at a rare outcome (disease) and you do a cohort study, you would need to follow a huge number of people (in your cohort) to identify enough cases to make any statistical inference. Does that make sense?
Thanks. It helps. Also, I think, if the outcome is rare and we do not have historical data, then we can do a prospective cohort study to gather the data and then we can conduct a Nested case-control within that cohort study. I think If we conduct a nested case-control then the issue with the sample size can be resolved as we proportion of case and control can be 1:1 or 1:2 or 1:4.
Hi Ahmed - the real difference lies in what it is that the two respective studies are trying to do. A case control study is always looking at knowing cases(outcomes) and exploring possible exposures (causes) and a cohort study is always looking at known exposures and exploring possible outcomes. So a retrospective cohort study will still start with a group (cohort) who were exposed to something and consider a variety of possible outcomes (a case control would look at one outcome and explore multiple exposures). Does that help?
+sss6538 hi there - in a cohort study (even if its retrospective) you're interested in the outcomes found in a specific group (your cohort). Case control studies are interested in the outcomes associated with a specific exposure
Yes, this video summed up the main points well. Just started a basic course to wrap up a M.S. in Clinical Nutrition. So, rare outcome (disease) and exposure with rare results for the exposed groups in both case control and cohort studies. Thanks.
Great video, I am having some trouble here with my results, and seeking for some orientation if it´s alright. Is the outcome in a case-control study necessarily a dichotomic variable (present / absent)? What should I do if my outcome is rather a continuous variable, since my exposure is a new surgical technique in evaluation for the cases, in comparison with a traditional method used in the controls? I have troubles to claim my controls non-demographically different from my cases; can I test with ANOVA and prove (in the best case) that cases and controls are no different from each other for x demographic variables? Is that a valid “pairing”? Thank you very much, as you can see a deadline is eating me alive!
Mauricio Martínez Moreno thanks for the question. I'm actually going to try to find someone who is working with these issues on a day to day basis to weigh in here and give you a good answer. (sorry for the delay).
Mauricio Martínez Moreno I am not sure what you mean by outcome being continuous. Case-control study is a type of study design where researcher identifies the affected (diseased) group and compares it to an unaffected group to investigate what exposure(s) was significant for the difference between the two groups. So in that sense, it is dichotomous, but you can also compare more than one group. How you define affected is not a concern of the design. If your outcome is diminished lung capacity and you measure it by a continuous scale, it is fine. there must still be a cut-off where comparison group is above/below that cut-off (or in a range). I fact, the groups maybe determined not only by one criteria but many continuous and discrete (i.e. an tumor size+histology+ln involvement). After that you can compare any explanatory variable between these two (or more) groups. The type of data determines what type of statistical method one uses. For instance, if your outcome is continuous (like IQ, performance, blood pressure etc), you would use linear regression, parametric or non-parametric test (depending on the data characteristics), and if it is discrete, then you use logistic regression, chi-square etc to test your hypothesis. Before deciding what statistical method to use, you need to decide what question you want to answer. Are you comparing two or more groups? What is your outcome measure? What measurement is more meaningful to the user of the results? etc. this is a quick simplified response; I hope it answers your question.
Ayse Tezcan Sure. Thank you very much for your clarifying answer. In fact, my outcome is continuous (extent of tumor resection as measured by a volumetric analysis) which gives a volume and a percentage of resection, among other values as tumor specific location, histology etc. Given that my sample was limited (n = 8 cases / 8 controls) because of the specific inclusion criteria, I decided to use a non-parametric test for two independent samples, so I used Mann-Withney U, with good results :) Thanks a lot, I considered for a while whether I should do the cut-off value to convert everything to dichotomic, or compare as I finally did.Thanks a lot for your kind support. Best regards from Viena.
How about genetic studies? Are the below scenarios all case control? Scenario 1: People with the power gene and people without it, get their power measured. Scenario 2: Elite power athletes vs non power athletes or norma people checked for prevalence of the power gene in the groups. Scenario 3: A group of people gets both gene and power tested in the present, and correlation is calculated between power and the Gene tested
I have one doubt , in cohort study if we are taking exposed group as one character and non exposed (comparing group) other character eg . exposed group as occupational cohort and non exposed with different cohort .or non exposed should also be the same cohort or not?
Exposed and non exposed need to be reflecting same variable/factor under study that is why some times we get to know if out of total diseased exposure is really associated withthe disease in question or not
There are 2 types of cohort studies: Prospective and Retrospective I am having difficulty in dofferentiating Retrospective cohort and Case-Control Can u help pls?
Its a common problem. Just remember, with a cohort study, you are interested in the "outcomes" and with a case-control study, you are interested in identifying "exposures"
The important thing to remember is that a cohort study is always looking at a group (a cohort) who have all been exposed to an identifiable exposure and we're still wanting to know if over time, what outcomes might be associated with that exposure. In the case of a retrospective cohort study, the timeline that we follow is in the past (and we have some record of who was exposed to what and what the respective outcomes were).
Get my FREE cheat sheets for Public Health, Epidemiology, Research Methods and Statistics (including transcripts of these lessons) here: www.learnmore365.com/courses/public-health-epidemiology-research-methods-and-statistics-resource-library
You really broke the differences between a case control and cohort study down very simplistically. Thank you!
The explanation of the subject matter was spot-on. Thanks Dr. Greg!
Concise and very helpful. I love the pictorial representation of the concepts!
Glad you liked it Jolene! Thanks for the feedback :)
Thanks.
May I pls request if you make a video about how to distinguish who you to involve and not to involve in calculating period prevalence.
Regards
one of the best tutorials on this subject brief yet concise!
Abdul Quadeer Mohammed thanks for the comment - much appreciated.
Thanks a lot, Sir. you made it so easy. It is so annoying that I have paid tuition fees for university and I still have to turn UA-cam upside down to understand every concept better.
Thank you for sharing your experience, and best of luck with your studies!
At school you are given all the information you need to pass the exam. University is next level learning. At the university level you 'read' for a degree. It means that you are given enough information to go on, then you are expected as an adult, to read around your topic independently to develop your own learning skills, which are critical life skills that you will use forever more. UA-cam is an excellent place to find extra information and Greg's site is a nice resource.
Muchas gracias por su excelente presentación. Saludos desde Ensenada, México.
Thanks Dr Greg, your explanation is clear and easy to understand. Straight to the point
Thanks for the feedback Gemini! Much appreciated. Have a great day.
Excellent explanation.
+Brendon Evans Thanks! Glad you liked it!
Thanks Brendon!
I have two questions to ask for those designs
1-When do we use case control study design?
2-when do we use cohort or longitudinal study design???
You did not explain the difference btween Case Control & Retrospective Cohort. Cohort has 2 types. That is the most confusing part you missed!
You saved my life! I finally understand the exact diffrences between these two. Thank you!
Happy to help! You are so welcome!
Many thanks for this video and all other efforts. I would like to ask about the Retrospective Cohort study ! as you mentioned it as a Prospective !
+Kahtan Thanks for the question. So Retrospective cohort studies can be a little confusing because, as you mentioned cohort studies are usually prospective. The important thing to remember is that a cohort study is always looking at a group (a cohort) who have all been exposed to an identifiable exposure and we're still wanting to know if over time, what outcomes might be associated with that exposure. In the case of a retrospective cohort study, the timeline that we follow is in the past (and we have some record of who was exposed to what and what the respective outcomes were).
hey! this is jennifer from 2020 and i just wanna say thank you for this video. great explanation!
Hi Greg -
In Kenneth J. Rothman's textbook; "Epidemiology: An Introduction (2nd edition)", Rothman talks about "Retrospective Cohort studies" (P.85). What is your take on that? He refers to a study conducted by Morrison et al. A study on data since 15th and 16th century in Florence.
It is quite confusing (not what I needed on top of the heap of other epidemiology confusion) :P
So awesome... Should have come here to learn this a long time ago. .
Thankyou for concisely highlighting important key points. Understanding of differences has been achieved....
Thanks for watching and you are welcome!
1That was a world class explanation!
Super helpful in studying for my biostatistics midterm! Thanks!
Thank you so much!! That was very descriptive and that made my studying easier.
Glad to hear that you liked the video Ricky Chow
Thank you for saving my exams and actually explaining what I was toiling on so hard
Happy to help! You are so welcome!
Excellent Video, short and Crip! love it!.. thanks a ton for your efforts!
+Kshitij Khanna THANKS for the comment
Super simple, thank you ! Good luck
Thank you but What about the difference between case control and retrospective cohort study?
What is the difference between a case control and a retrospective cohort study.
What is the diference between case control study and a retrospective cohort study?
What is the difference between retrospective cohort and case control?
What are the differences between the case-control study and a retrospective cohort study?
From India,your explanation is marvelous.. i liked it a lot....
Glad you liked it
I read some research papers use retrospective cohort study, how about that? What's the difference?
what about a retrospective cohort studies ? its seems like you have exclude their existence ?
I am watching it 2024 the best professor ever for epi and statistics
Thank you for your kind words, and happy learning!
You saved a poor medical student from a small headache, thank you
Glad it was helpful! Thanks!
Hi Greg. I am confused between retrospective cohort studies and case control studies. It seems like in both situations you look at people with a disease and people without a disease and then look back at exposure?
Could you please explain the difference?
Really thanks as I get the clear explanation.
Can you give us an example for sake of deeper understanding when would you choose retrospective cohort and when would you choose case-control and under which circumstence would you choose one over other for a given problem?
Hi there - if you are looking at a rare condition - lets say hypothetically, people whose hair turned blue - you might want to consider a range of possible exposures that could have caused this. You'd look at diet, exposure to sunshine, genetics, the type of shampoo that they use etc. etc. (that would be a case control study). Start with the cases and look back at possible exposures. In a retrospective cohort (as in with any other cohort) your starting point is an exposure (not an outcome). You might for example be interested in what diseases have emerged following exposure to the radiation in Japan. There might be any number of outcomes. Your cohort is the group of people exposed. In this case however, the exposure is in the past (making it retrospective). Does that make sense?
Yes i finally think i do get it . If we have a known diesese but haven't figured out the causes yet, we will go with case-control, but if we have a known cause but we yet have to proove which diesese it can cause we will go with retrospective cohort.
That's it!
Could you do a video on Attributable Risk, Absolute Risk Reduction (ARR), Number Needed to Treat (NNT), and Number Needed to Harm (NNH). These topics are all very similar and get confused. THANKS FOR YOUR VIDEOS!
Joseph Reinshagen will do.... thanks for the suggestion!!
Wow amazing short and precise
+tarie ruvibez THANKS!
ok, so in case case control, we already have the outcome and we want to find out what exposures lead to the outcome. so this study does access temporality right
Yes, in the sense that the exposures being examined need to precede the outcome that you've identified in your cases.
Amazing demonstration ...
thank you a lot
+abedalla h You are most welcome
so good I wished I found this channel sooner
धन्यवाद जी।
👏👏
thank you so much for this video it helped me in my homework for the epidemiology class..
you provided the information in a very easy and interesting way!!
Glad I could help
Wau
great explanation :) i came here lookin for the difference between case control study and RETROSPECTIVE cohort study . unfortunately i coudnt get it
Valuable information ،
thank you
Glad it was helpful! You're welcome :)
Fantastic! I shared this with my students.
Thanks for letting me know Marjorie Simpson (much appreciated). What are you students studying (and where)? Please let them know that they are welcome to get in touch with me if they have suggestions re future video content on this channel. I also host a weekly "live" global health news roundup every Wednesday at 2pm (EST) which that might be interested in. Find out more at www.twigh.org
how about retrospective cohort
in cohort study; if the exposures get disease due to exposure, how did the non exposure get disease. any help
The cohort studies can be retrospective (much less common though) too. Ohterwise great summary!
True. thanks for the input. :)
Wonderfully explained! Super clear. Thanks a lot.
+Camila C thanks for the feedback - much appreciated.
Please can you explain the difference between a retrospective cohort study and case control study? I want to study exposure on an outcome of interest. For e.g I want to use health data and examine whether use of drug A prevents hospital admissions for group of infectious disease.
+MsZa124 Thanks for the question - it can be confusing. Regarding a cohort study - don't worry about whether or not its prospective or retrospective, the principle remains the same... you are looking at a range of possible outcomes in a defined groups (a cohort). That group is sometimes defined by a particular exposure (like whether or not they took Drug A - to use your example). Individuals in the group (cohort) may or may not become ill, or have some other outcome of interest. By contrast, in a case control study, your starting point is a group of people who are "cases" (who definitely DO have the outcome of interest). By comparing them to the controls you can establish whether or not there was a significant difference in their relative exposure to a number of risk factors. To answer your question, I guess it comes down to this: are you looking at just one drug with multiple possible outcomes (in which case you want to do a retrospective cohort study) or are you looking at a particular outcome (whether or not the person got an infectious disease) and you want to consider multiple possible exposures (in which case you want to do a case control study). It can be confusing. I hope this helps.
+Global Health with Greg Martin thank you for the clear response. It makes sense to me now :)
+MsZa124 I always say that the difference between a retrospective cohort and a case-control study is your defined baseline. In a case-control, you are looking today at a sample of diseased and non-diseased individuals, and asking them to recall exposures in their past (retrospective). In a retrospective cohort, you are also going back in time, but to a defined baseline point in time that happened in the past (e.g., all births in 2003). You will then follow your defined baseline point of time forward in time (e.g., 2003-2013) via records and secondary data to examine the difference in risk/outcome onset by exposure status. Hope that helps!
+Holmesymom Thank you for expanding on this. Very helpful :)
Thank you for this video! I am studying for my USMLE Step 1.. THIS HELP ALOT!!!
Glad it helped Joseph Reinshagen - good luck with the exams!
Thank you so much, i was giving up on understand this topic
Happy to help!
i dont understand then whats the difference between a case control study and a cohort "Retrospective" study ?
This is so concise!! Thank you very much!
Thanks for the feedback. Much appreciated.
Excellent explanations please add the full contents about research
Thanking you
Thanks Muhammed - will do. Happy day. Greg
short and precise. Great job
wow great explaination.in such a simple way !!!!
Very simplified and useful.
Dear Greg, thank you for this educational video. I have a quick question: how long would you recon a cohort study should last? If you write a thesis in about a year is it realistic? Or should it last over a number of years/decades?
Thanks for the question. The truth is that it's kinda like a piece of string... It's as long as it needs to be. That is to say, it depends on what's you're wanting to observe in your cohort. You may be looking at outcomes that take years to present (like cancer) or days (like the common cold). Hope that helps.
sir in cohort study how can confounding factors know
Really helpful! The explanation is very easy to understand. Thank you for this educational video!
I'm delighted that you found it easy to understand. Thanks for the feedback Huy.
Hello!
I have a question. Can you explain, why prospective cohort is not good for rare diseases and retrospective cohort is not good for very rare diseases? I know for rare outcomes, we should conduct case control studies. But what if, the outcome is rare but we do not have any historical data to conduct a case control study. Then in a hypothetical situation where funding is not a problem, what approach should we take?
Hi Ahmed - its a great question. On the whole, a cohort study is considered better than a case control study but it is sometimes not practical. So for example, if you are wanting to look at a rare outcome (disease) and you do a cohort study, you would need to follow a huge number of people (in your cohort) to identify enough cases to make any statistical inference. Does that make sense?
Thanks. It helps. Also, I think, if the outcome is rare and we do not have historical data, then we can do a prospective cohort study to gather the data and then we can conduct a Nested case-control within that cohort study. I think If we conduct a nested case-control then the issue with the sample size can be resolved as we proportion of case and control can be 1:1 or 1:2 or 1:4.
very useful, thank you, Dr. Greg!
Sir Can we have something on Sampling
How can we differentiate between retrospective cohort and case control?
Hi Ahmed - the real difference lies in what it is that the two respective studies are trying to do. A case control study is always looking at knowing cases(outcomes) and exploring possible exposures (causes) and a cohort study is always looking at known exposures and exploring possible outcomes. So a retrospective cohort study will still start with a group (cohort) who were exposed to something and consider a variety of possible outcomes (a case control would look at one outcome and explore multiple exposures). Does that help?
Yes, Thanks a lot.
what is the difference between
retrospective cohort study >> and
+sss6538 hi there - in a cohort study (even if its retrospective) you're interested in the outcomes found in a specific group (your cohort). Case control studies are interested in the outcomes associated with a specific exposure
Awesome presentation.
I appreciate the feedback. Thanks.
Your videos are amazing!
Glad you like them! Thanks Nida!
Yes, this video summed up the main points well. Just started a basic course to wrap up a M.S. in Clinical Nutrition. So, rare outcome (disease) and exposure with rare results for the exposed groups in both case control and cohort studies. Thanks.
Glad you enjoyed the video Charlien!
Clear so far, but missing case cohort.
Thank you so much
You're most welcome
Amazing Sir .. you are a perfect Teacher
Thats a really nice compliment manuboon boon - much appreciated!
Very helpful! Thank you!
Glad it was helpful!
what z difference btw retrospective cohort and case control????
Thank you sir, it's a clear explanation
You're most welcome Jonathan.
very clear tutorial. Thank u
Super helpful, thank you
Thanks, this helped me a lot!
Glad to hear it! Thank you.
Greg, this is a great supplement to my global health education, thanks so much for your time and effort.
Glad you liked the video Rory Watts - please feel free to send me any thoughts or ideas about future content for the UA-cam channel.
Great video, I am having some trouble here with my results, and seeking for some orientation if it´s alright. Is the outcome in a case-control study necessarily a dichotomic variable (present / absent)? What should I do if my outcome is rather a continuous variable, since my exposure is a new surgical technique in evaluation for the cases, in comparison with a traditional method used in the controls?
I have troubles to claim my controls non-demographically different from my cases; can I test with ANOVA and prove (in the best case) that cases and controls are no different from each other for x demographic variables? Is that a valid “pairing”?
Thank you very much, as you can see a deadline is eating me alive!
Mauricio Martínez Moreno thanks for the question. I'm actually going to try to find someone who is working with these issues on a day to day basis to weigh in here and give you a good answer. (sorry for the delay).
Global Health with Greg Martin Great! Thanks a lot.
Mauricio Martínez Moreno I am not sure what you mean by outcome being continuous. Case-control study is a type of study design where researcher identifies the affected (diseased) group and compares it to an unaffected group to investigate what exposure(s) was significant for the difference between the two groups. So in that sense, it is dichotomous, but you can also compare more than one group. How you define affected is not a concern of the design. If your outcome is diminished lung capacity and you measure it by a continuous scale, it is fine. there must still be a cut-off where comparison group is above/below that cut-off (or in a range). I fact, the groups maybe determined not only by one criteria but many continuous and discrete (i.e. an tumor size+histology+ln involvement). After that you can compare any explanatory variable between these two (or more) groups. The type of data determines what type of statistical method one uses. For instance, if your outcome is continuous (like IQ, performance, blood pressure etc), you would use linear regression, parametric or non-parametric test (depending on the data characteristics), and if it is discrete, then you use logistic regression, chi-square etc to test your hypothesis. Before deciding what statistical method to use, you need to decide what question you want to answer. Are you comparing two or more groups? What is your outcome measure? What measurement is more meaningful to the user of the results? etc. this is a quick simplified response; I hope it answers your question.
Ayse Tezcan Thanks for your input on this.
Ayse Tezcan
Sure. Thank you very much for your clarifying answer. In fact, my outcome is continuous (extent of tumor resection as measured by a volumetric analysis) which gives a volume and a percentage of resection, among other values as tumor specific location, histology etc. Given that my sample was limited (n = 8 cases / 8 controls) because of the specific inclusion criteria, I decided to use a non-parametric test for two independent samples, so I used Mann-Withney U, with good results :) Thanks a lot, I considered for a while whether I should do the cut-off value to convert everything to dichotomic, or compare as I finally did.Thanks a lot for your kind support.
Best regards from Viena.
How about genetic studies?
Are the below scenarios all case control?
Scenario 1: People with the power gene and people without it, get their power measured.
Scenario 2: Elite power athletes vs non power athletes or norma people checked for prevalence of the power gene in the groups.
Scenario 3: A group of people gets both gene and power tested in the present, and correlation is calculated between power and the Gene tested
This video was very helpful. Thank you! :)
+MsZa124 you are most welcome!
Thanks a lot!
You're welcome!
sir, here what is meant by exposure and non exposure??????????
Hi there - thanks for the question. by "exposure" we mean people that have come into contact with a risk factor that might cause disease.
Helpful, thank you.
You are most welcome Misk Fahad
I have one doubt , in cohort study if we are taking exposed group as one character and non exposed (comparing group) other character eg . exposed group as occupational cohort and non exposed with different cohort .or non exposed should also be the same cohort or not?
Exposed and non exposed need to be reflecting same variable/factor under study that is why some times we get to know if out of total diseased exposure is really associated withthe disease in question or not
Very helpful thanks
super explanation!
Cheers
You forgot to do retrospective cohort study
Thank you very much, you solve my problem
So happy to help! Thanks
There are 2 types of cohort studies: Prospective and Retrospective
I am having difficulty in dofferentiating Retrospective cohort and Case-Control
Can u help pls?
Its a common problem. Just remember, with a cohort study, you are interested in the "outcomes" and with a case-control study, you are interested in identifying "exposures"
Great explanation sir
Rajeev Midha thanks :)
hi. wats d difference between retrospective cohort and case control
The important thing to remember is that a cohort study is always looking at a group (a cohort) who have all been exposed to an identifiable exposure and we're still wanting to know if over time, what outcomes might be associated with that exposure. In the case of a retrospective cohort study, the timeline that we follow is in the past (and we have some record of who was exposed to what and what the respective outcomes were).
thank u
Superb!! Excellent!!
Glad you liked it! :)
Hey Greg are you from South Africa ?
reardelt yes indeed! I am actually in JHB for the next two weeks. Living in Dublin but am a South African. :)
Very much appreciated.
Thanks Iman Awad
Hey Sir thanks for this.
I finally understand 🤯, thank you 😭🙏🏿