PT54.S4.Q20 - tv meteorologist: our station's weather

civnetn

https://7sage.com/lsat_explanations/lsat-54-section-4-question-20/
Could someone please explain why answer A is correct. I can get there by process of elimination as I understand fully why the other answers are incorrect. But I'd really like to understand the reasoning between A so I can say I have a "full understanding" of this question. It would be helpful if someone could give an example using numbers.

Accounts Playable

This has always been one of my favorite questions ever to appear on the LSAT; good old Bayes' Rule.

Here's a short paraphrase of the argument:
In this community, what matters most is for the weather forecast for rain be correct. Most of the time, when we forecast rain for the following day, it actually rains. Our competitors don't share this statistic. Therefore, our weather forecasts are better than the competitors.

What I'm looking for: This is essentially a disguised conditional probability problem. Think of this example: say we are talking about a 100 day period, and over those 100 days, say it actually rains like 60 times.

Our weather station is ultraconservative and only forecasts rain once (when we are 100% certain, which might be not that useful since it might be obvious that it's going to rain). We have a 100% accuracy rate! We predicted rain for one day and it did rain the next day! But, we missed the other 59 times! Say the competitors predicted rain at a 49% accuracy rate: it correctly predicted 29 out of the 60 times. Doesn't that seem much more useful (even if the "accuracy rate" is less than 50?) It correctly warned the residents more frequently for rain.

Answer A strengthens the argument because it denies this possibility. If our weather station predicts more rain that the competitors, then the 50+% accuracy rate is not only a higher percentage, but also a higher number of correct predictions.

civnetn

@"Accounts Playable" Thanks so much for this explanation. I usually frequent the Manhattan LR forums to see explanations and none of the 11 replies were as remotely helpful as yours. In fact, they made what is really a simple problem, incredibly more complex. This makes so much more sense.

I suppose my confusion came from wanting (A) to be worded as, "The meteorologists station forecast rain correctly more often than did..."

I should have realized that since I'm supposed to take what's in the stimulus as true, any increase in the number of forecasts from the meteorologist's station would necessitate an increase in correct forecasts, proportional to greater than 50% of the forecasts.

Andrew_Neiman

My prephrase was what if accuracy on most important question for viewers =/= more useful and reliable than the competition? I went into the answers hoping to find an answer that said more accuracy means more reliable than competitors. Is this not the right thinking? I'm having a lot of trouble adjusting my weaken analysis into Strengthen for some reason. I'd appreciate any help. #help