Scioly.org

Also, though, I get 2.1 for the risk from goulash - 20/21 divided by the baseline, which is 45/99 if I am reading your table correctly.

Flavorflav- can you explain your method of calculating RR in a situation like this- or at least what do you use as your baseline?

You mentioned this method might be incorrect in a real study, in which case- what is the appropriate way to calculate RR?

Another general question about RR- will/should it always be around 1, or can you end up with >1?

ironchef48 wrote:

Also, though, I get 2.1 for the risk from goulash - 20/21 divided by the baseline, which is 45/99 if I am reading your table correctly.

Flavorflav- can you explain your method of calculating RR in a situation like this- or at least what do you use as your baseline?

You mentioned this method might be incorrect in a real study, in which case- what is the appropriate way to calculate RR?

Another general question about RR- will/should it always be around 1, or can you end up with >1?

If you don't end up with something that is greater than one, you probably did something wrong - especially this year, when you are likely to be asked to determine which of several food items is responsible for the food poisoning. Whichever it is should have an RR well over one.

As for the baseline issue, like I said before in most studies you are interested in a single factor and you are comparing two populations, one exposed population and one unexposed - for example, smokers and nonsmokers. With food poisoning, though, you are often looking at the same population (i.e., all the people at the picnic), so you generally want to use all picnic goers as your baseline and compare the attack rate for each food item against the aggregate attack rate. I was able to find a source that compared exposed to unexposed for a each factor, though, so I can't say that it is wrong (in fact, there is an awful lot of inconsistency in epidemiology - look at the way the term Relative Risk is used, for example); it's more that most of the time, comparing exposed to unexposed for each item reduces the size of your groups to the point where statistical examination becomes less meaningful. I have also seen events in which they want you to use the lowest risk group as your baseline - this is most common when you are dealing with a personal characteristic such as age or gender, but could be used for other variables of interest. The most important thing is always going to be careful reading, though - in a good event, the writer will specify the baseline they want you to use. If they don't, a good grader would give you full credit for any valid baseline, but in my experience good graders of this event are few and far between. Unfortunately, that means that you have to make your best guess at the baseline they want you to use, and the odds are that if you pick the wrong one, you will lose a lot of points.

The Disease Detectives Division B Varsity exam was not too difficult. But, the case studies were brain-benders... The rest was easy. Good luck to everyone!!!

What is the difference between a prospective cohort and a case control study?

Check the Wiki on DD it might give you the answer... I'm not sure.

They seem similar, but a cohort study starts with healthy individuals and assesses response to exposure (or lack thereof), while a case control study starts with individuals with the disorder, and collects historical data.

kjhsscioly wrote:They seem similar, but a cohort study starts with healthy individuals and assesses response to exposure (or lack thereof), while a case control study starts with individuals with the disorder, and collects historical data.

While not inaccurate that is a bit misleading, since a retrospective cohort also looks at historical data. The key distinction is that a cohort study follows a defined group over time, either really (as in the prospective cohort) or virtually (in the retrospective). A case-control is more of a snapshot, comparing cases to controls for some factor of interest. There is usually only one defined group in a cohort study, since you are generally comparing + and - for some factor within the cohort, while a case-control study always has at least two groups - the cases and the controls.

Are there any "giveaways" for different study designs?
I'm mainly looking for obvious characteristics of:

Ecological
Case-control
Cohort
Randomized controlled Trial

Thanks!

Also, does anyone have a good list of Food Borne Illnesses?

EpicFailure wrote:Are there any "giveaways" for different study designs?
I'm mainly looking for obvious characteristics of:

Ecological
Case-control
Cohort
Randomized controlled Trial

Thanks!

Also, does anyone have a good list of Food Borne Illnesses?

I think there is a list of food borne illnesses on the CDC website. Otherwise, I would suggest starting with the three most common (campylobacter, e. coli, and salmonella) and work your way down to least common.

Hey does anyone have the formula for Sensitivity and Specificity?