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Private Wang Fire wrote:

Unome wrote:

Private Wang Fire wrote:
Cohort presumes that you are tracking the entire exposed/unexposed population to the outcome, whether they develop the disease or not. Case-control starts with the outcome, so when you go back towards whether they were exposed/unexposed, you don't have the whole population, just a sample. Does this make sense? I'm not a very clear explainer

So why can a cohort study generalize a determined relative risk to a broader population of people? (or can it just not?)

The "population" in the case of a cohort is the entire exposure group, as in everyone who was exposed to that specific exposure at the specific time and place in the case study, which means relative risk can be used.

In the case control, the cases or controls you select initially represent only part of the total "population" that you're studying - population in this case would be defined to strictly those with nearly identical (in an ideal case) characteristics and the only thing that sets the two groups in the study apart would be whether they were exposed or not.

So not like a broader population of people, just like the population that is involved in the disease 'event' or whatever.

Another thing you might want to consider when thinking about this is that cohort studies are trying to find a disease, and case-control is trying to find a exposure

cookie75 wrote:

Private Wang Fire wrote:

Unome wrote: So why can a cohort study generalize a determined relative risk to a broader population of people? (or can it just not?)

The "population" in the case of a cohort is the entire exposure group, as in everyone who was exposed to that specific exposure at the specific time and place in the case study, which means relative risk can be used.

In the case control, the cases or controls you select initially represent only part of the total "population" that you're studying - population in this case would be defined to strictly those with nearly identical (in an ideal case) characteristics and the only thing that sets the two groups in the study apart would be whether they were exposed or not.

So not like a broader population of people, just like the population that is involved in the disease 'event' or whatever.

Another thing you might want to consider when thinking about this is that cohort studies are trying to find a disease, and case-control is trying to find a exposure

Another good way to think about it is by looking at the purposes each of the studies have. In a cohort study, you're typically trying to figure out the probability (or risk) of developing a common disease from a fairly specific exposure (e.g. risk of getting cancer if you are exposed to high levels of a certain brand of pesticides) - your population then is going to be only those that are exposed, so that you can say "well all of these people were exposed to the pesticide and five of them developed cancer, so there's probably an association (or not)".

In a case-control study, you work the opposite way - you work backwards from a fairly specific outcome or disease to an exposure. This is especially common when studying a foodborne-illness outbreak, where you're trying to determine which exposure (menu item or ingredient) was the most probable cause of the outbreak. Because of this, your population is going to be, as Private Wang said, all the people "involved in the disease event or whatever" (all the people who ate at the restaurant during the designated period of time). This is also why you use odds ratio instead of risk - with an odds ratio you're trying to determine which of the exposures was the most probable cause of the outcome, but with risk and cohorts you're trying to determine the probability that an exposure will cause a certain disease.

Do you know what diseases we need to study? Is there a list? What do we need to know from each of the diseases? Thanks in advance!

parvatipatel wrote:Do you know what diseases we need to study? Is there a list? What do we need to know from each of the diseases? Thanks in advance!

This event is less about specific diseases and more about the procedures used to investigate disease outbreaks; process skills with epidemiology vs. in-depth content knowledge. The Disease Detectives Wiki should give you a good intro.

It's a tough call. While this is not a taxonomy event, it's expected that there'll be topical stuff on every well-prepared test. And, there are a small handful or two of relevant pathogens to this year's topic(s) such that I'd recommend knowing them in enough detail (or, at least, dumping that information in a corner of the cheat sheet). The training handout contains a table you may find helpful.

So you would not give a description to each 57 pathogens that make foodborne illnesses?

Yeah, that's excessive. Extra background knowledge can give you an edge once in a while, but I wouldn't burn cheat sheet space on 57 pathogens where you probably don't need to know about 56 of them when there is plenty of epi-specific stuff to focus your attention on that is more likely to help you here. A well-written test isn't going to go into that level of depth on these things. Anyway, the training handout table contains sixteen pathogens. I'd spend maybe one practice's worth getting acquainted with them and direct your focus back to the epi stuff thereafter.

parvatipatel wrote:Do you know what diseases we need to study? Is there a list? What do we need to know from each of the diseases? Thanks in advance!

These might be a helpful list to review or put on your cheat sheet
http://www.fda.gov/Food/FoodborneIllnes ... efault.htm

This is a question that pertains to both microbes and disease for which I have never found a quality answer: What is the difference in diseases caused by bacteria and diseases caused by viruses? Obviously their causative agents differ, but how do the general characteristics differ? For example, does one tend to cause certain different symptoms?

I have looked online for this, and the only things I can find are websites that list characteristics of viruses and bacteria and websites that give examples of diseases caused by each. (And obvious stuff like the fact that antibiotics don't work against viruses).

SOnerd wrote:This is a question that pertains to both microbes and disease for which I have never found a quality answer: What is the difference in diseases caused by bacteria and diseases caused by viruses? Obviously their causative agents differ, but how do the general characteristics differ? For example, does one tend to cause certain different symptoms?

I have looked online for this, and the only things I can find are websites that list characteristics of viruses and bacteria and websites that give examples of diseases caused by each. (And obvious stuff like the fact that antibiotics don't work against viruses).

Diseases caused by bacteria are due to the toxins that bacteria excrete, while viruses hijack the hosts cells by inserting genetic material into the cells. Symptoms depend on the individual microbe causing the sickness, and how your body tries fighting it off

Hope I helped!