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Attack ratio and Postitive predictive value

I am having diffiuculty with 2 questions.

1. Does specificity, or prevalence have a greater effect on positive predicitve values (PPV)?

2. 200 people at a dinner. 122 people get sick. 150 (of the 200) had ice cream- 118 got sick,

while- 50 (of the 200) had pie- 4 got sick.

Which desert was responsible for the illness, and why?

I used the ATTACK RATIO, to determine that the ice cream casued people to get sick

AR(ice cream)= 79%, AR (pie)= 8%. Am I correct and how do I wrtie why?

Solution Preview

(1). Prevalence will have a greater effect on positive predictive values. The prevalence of a test is much lower so the predictive value of a positive test will also be lower. As ...

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