by cwyoo » Wed Jan 24, 2018 4:41 pm
Before the mad cow disease epidemic in the mid-1990s, few people had heard of Creutzfeldt-Jakob disease (CJD). That's because Creutzfeldt-Jakob disease, an invariably fatal, degenerative brain disorder, has always been considered rare. Worldwide, doctors typically diagnose one case of Creutzfeldt-Jakob disease per million people each year, most commonly in older adults.
That changed decades ago when an unusually large number of people in Great Britain developed what appeared to be CJD. Most were relatively young, and all had eaten meat from cattle suspected of having bovine spongiform encephalopathy (BSE), the medical term for mad cow disease.
Scientists eventually concluded that the new ailment — named variant CJD (vCJD) — was a form of CJD resulting from exposure to BSE. Since then, a number of cases of vCJD have been linked to contaminated beef in Great Britain and in other countries, including Spain, Portugal, France and Germany.
Although "classic" Creutzeldt-Jakob disease hasn't been linked to infected beef, it's similar to vCJD in many respects. No treatment exists for either type of CJD, and nothing can slow the progression of the disease (from Mayo Clinic).
Let’s say if someone has vCJD, there is 95% chance that person will show paralysis and if someone does not have vCJD, there is 3% chance that person will show paralysis.
(a) What is the probability having paralysis and not vCJD?
(b) You come across a person who shows paralysis in US. What is the probability that this person has vCJD (assume there is one case of vCJD per million people in US)?
(c) What is the probability that the person in (b) has vCJD if he or she turns out to be a tourist from Great Britain (assume there is one case of vCJD per 100,000 people in Great Britain)?
(d) Discuss the limitation of your calculations on (a), (b), and (c).