## Disease Detectives B/C

Nerd_Bunny
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### Re: Disease Detectives B/C

Froggie wrote:
UTF-8 U+6211 U+662F wrote:Is it just me or does every test have a matching section on the same fourteen or so terms

I’ve seen this a lot, it’s usually epidemic-endemic-pandemic-otherstuff. (There was this one test with a matching section about 30 questions long. It took a long time.)

At the NEBO invitational our test had about 100 terms that we had to define and provide examples for. I only got to 50 of them (each worth just one point) when I realized it would be better to help my partner with the rest of the test.
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### Re: Disease Detectives B/C

Can you guys give me a simple criteria to write a case definition. It's my hardest thing to do
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### Re: Disease Detectives B/C

Killboe wrote:Can you guys give me a simple criteria to write a case definition. It's my hardest thing to do

If you just put down some info for person, place, time, and clinical, you should get full points.
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### Re: Disease Detectives B/C

Does anyone have any info on the quality of the Disease test for Div B nats?
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### Re: Disease Detectives B/C

wzhang5460 wrote:Does anyone have any info on the quality of the Disease test for Div B nats?

It's hard
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Froggie
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### Re: Disease Detectives B/C

Asking questions a week before states yay
1). Should attack rate be in a percentage form? Should relative risk be in percentage form? Should odds ratio be in percentage form?
2). This was a question on a test: Number ill and exposed = 51, Number not ill and exposed = 34, Number ill and not exposed = 2, number not ill and not exposed = 13. The answer sheet says that the attributable risk is 46.67%, but I keep getting 362%. Can someone explain?
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### Re: Disease Detectives B/C

Froggie wrote:Asking questions a week before states yay
1). Should attack rate be in a percentage form? Should relative risk be in percentage form? Should odds ratio be in percentage form?
2). This was a question on a test: Number ill and exposed = 51, Number not ill and exposed = 34, Number ill and not exposed = 2, number not ill and not exposed = 13. The answer sheet says that the attributable risk is 46.67%, but I keep getting 362%. Can someone explain?

1) AFAIK it doesn't matter, but I would just use numbers.
2) (51/85) - (2/15) = 0.4667 = 46.67%

Nerd_Bunny
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### Re: Disease Detectives B/C

wzhang5460 wrote:Does anyone have any info on the quality of the Disease test for Div B nats?

Last year the test was very long and very thorough. There weren't as many calculations as we expected there to be, but it was a very good test with two good-sized cases. They gave you all the information you needed, then asked you questions about it. All of them followed the rules, as far as I could tell, so we were really pleased with the quality of the test. I don't know about this year's test- I'm unsure if the proctor was from Wright State or will be also writing the test for this year.
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### Re: Disease Detectives B/C

Froggie wrote:1). Should attack rate be in a percentage form? Should relative risk be in percentage form? Should odds ratio be in percentage form?

As far as I know, attack rate should be in percentage form, while relative risk and odds ratio should not.
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UTF-8 U+6211 U+662F
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### Re: Disease Detectives B/C

Since the tables are 2x2 anyway, why not just do a 2-proportion z-test instead of a chi-squared test of homogenity?
Last edited by UTF-8 U+6211 U+662F on April 21st, 2018, 4:59 pm, edited 1 time in total.

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### Re: Disease Detectives B/C

UTF-8 U+6211 U+662F wrote:Since the tables are 2x2 anyway, why not just do a 2-proportion z-test instead of a chi-squared test of homogenity?

Pretty sure a z-test wouldn't work because of how the individuals are assigned to categories (e.g. what would your standard deviation be?)
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UTF-8 U+6211 U+662F
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### Re: Disease Detectives B/C

Unome wrote:
UTF-8 U+6211 U+662F wrote:Since the tables are 2x2 anyway, why not just do a 2-proportion z-test instead of a chi-squared test of homogenity?

Pretty sure a z-test wouldn't work because of how the individuals are assigned to categories (e.g. what would your standard deviation be?)

$H_0: p_{\textrm{exposed}} = p_{\textrm{not exposed}}$
$H_a: p_{\textrm{exposed}}$ (is not equal to or greater than or less than, depending on the question) $p_{\textrm{not exposed}}$
$\hat{p}_C = \frac{x_{\textrm{exposed}} + x_{\textrm{not exposed}}}{n_{\textrm{exposed}} + n_{\textrm{not exposed}}}$
$\sigma_{\hat{p}_{\textrm{exposed}} - \hat{p}_{\textrm{not exposed}}} = \sqrt{\frac{\hat{p}_C(1-\hat{p}_C)}{n_{\textrm{exposed}}}+\frac{\hat{p}_C(1-\hat{p}_C)}{n_{\textrm{not exposed}}}}$
$z = \frac{(\hat{p}_{\textrm{exposed}} - \hat{p}_{\textrm{not exposed}}) - 0}{\sigma}$
Not sure if pooling the proportions is absolutely necessary.

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### Re: Disease Detectives B/C

UTF-8 U+6211 U+662F wrote:
Unome wrote:
UTF-8 U+6211 U+662F wrote:Since the tables are 2x2 anyway, why not just do a 2-proportion z-test instead of a chi-squared test of homogenity?

Pretty sure a z-test wouldn't work because of how the individuals are assigned to categories (e.g. what would your standard deviation be?)

$H_0: p_{\textrm{exposed}} = p_{\textrm{not exposed}}$
$H_a: p_{\textrm{exposed}}$ (is not equal to or greater than or less than, depending on the question) $p_{\textrm{not exposed}}$
$\hat{p}_C = \frac{x_{\textrm{exposed}} + x_{\textrm{not exposed}}}{n_{\textrm{exposed}} + n_{\textrm{not exposed}}}$
$\sigma_{\hat{p}_{\textrm{exposed}} - \hat{p}_{\textrm{not exposed}}} = \sqrt{\frac{\hat{p}_C(1-\hat{p}_C)}{n_{\textrm{exposed}}}+\frac{\hat{p}_C(1-\hat{p}_C)}{n_{\textrm{not exposed}}}}$
$z = \frac{(\hat{p}_{\textrm{exposed}} - \hat{p}_{\textrm{not exposed}}) - 0}{\sigma}$
Not sure if pooling the proportions is absolutely necessary.

Ok, per internet research z^2 = chi-squared, which is interesting.
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### Re: Disease Detectives B/C

But with a two-proportion z-test, you get the freedom of doing one-tailed tests

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### Re: Disease Detectives B/C

UTF-8 U+6211 U+662F wrote:
Froggie wrote:Asking questions a week before states yay
1). Should attack rate be in a percentage form? Should relative risk be in percentage form? Should odds ratio be in percentage form?
2). This was a question on a test: Number ill and exposed = 51, Number not ill and exposed = 34, Number ill and not exposed = 2, number not ill and not exposed = 13. The answer sheet says that the attributable risk is 46.67%, but I keep getting 362%. Can someone explain?

1) AFAIK it doesn't matter, but I would just use numbers.
2) (51/85) - (2/15) = 0.4667 = 46.67%

I'm certain that attack rate is a percentage. As for odds ratio and relative risk, they are shown as decimal numbers as a ratio to 1. For example, an odds ratio or relative risk could be 43 as in 43 to 1.
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