PT8.S1.Q13 - Five years ago, during the North American outbreak...

uchennan27

Can someone explain to me why D is the right answer? I chose B, but I did not feel very strongly about its accuracy.

Burden.of.Floof

D is the correct answer, because it offers an alternative explanation for the increase in the percentage of deaths. The stimulus says that a smaller percentage of cows died from this disease 5 years ago than now. They therefore conclude that the virus is more deadly, which relies on the assumption that more cows have died. But if the deaths are piece of the pie (the total number of infected cows), the entire pie needs be the same from 5 years ago to now in order to draw the conclusion that they draw. This is a numbers don't equal percentages flaw. What if it were the case that the pie from 5 years ago included every single case that actually existed and the pie now only consists of the really, really serious cases that are far more likely to result in death? That's what answer choice D is saying.

McBeck418

Let's assume that during the first outbreak, there were 1000 reported cases and 5 per cent (50) died whereas now, 18 per cent died. The stimulus wants us to assume that the total number of cases remained the same. So during the first outbreak there were 50 deaths and in the second, there were 180 deaths. If that were the case, then we could clearly state the virus is more deadly. But we can't assume that the number of reported disease remained the same over time.

Answer B. says that in the first outbreak, many of the reported deaths were actually caused by some other virus. If that were the case, then even fewer of the deaths would be caused by this virus and if it's true that 18 per cent of current cases are dying, that's really bad. That seems to suggest that this virus really is more deadly. The first out break had 50 deaths in total , but some of those weren't from the virus. So less than 50 deaths to 180 is a big jump.

Answer D says that they were able to treat milder cases and no longer report them. So, I think there's two things happening here. First, our sample shifts. If people are no longer reporting mild cases, it sounds like the cases that are reported are more severe. What if we are now focusing on a subset of animals that are more likely to die. This doesn't mean the virus is more deadly.

Second, we have the percent/numbers. Without knowing the total number of reported cases, the percentages don't tell us that much. For instance, if there were originally 1000 reported cases that led to 50 deaths and now there are 200 reported cases and 36 deaths, we can't easily conclude that the disease is more deadly than it was before. Even if the death rate is increasing, it does not prove that the virus is more virulent.