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The number of people diagnosed as having a certain intestinal disease has dropped significantly in a rural county this year, as compared to last year. Health officials attribute this decrease entirely to improved sanitary conditions at water-treatment plants, which made for cleaner water this year and thus reduced the incidence of the disease.
Which of the following, if true, would most seriously weaken the health officials' explanation for the lower incidence of the disease?
| Text from Passage | Analysis |
| The number of people diagnosed as having a certain intestinal disease has dropped significantly in a rural county this year, as compared to last year. |
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| Health officials attribute this decrease entirely to improved sanitary conditions at water-treatment plants, which made for cleaner water this year and thus reduced the incidence of the disease. |
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The argument starts with an observation (disease diagnoses dropped significantly) and then presents the health officials' explanation for why this happened (improved water treatment led to cleaner water, which reduced disease incidence).
Health officials believe that improved sanitary conditions at water-treatment plants caused the significant decrease in intestinal disease diagnoses.
The officials use a simple cause-and-effect relationship: they see cleaner water as the direct cause of fewer disease cases. Their reasoning follows this chain: better water treatment → cleaner water → less disease transmission → fewer diagnoses. The word 'entirely' shows they think this is the complete explanation.
Weaken - We need to find information that would reduce our belief in the health officials' explanation that improved water treatment caused the drop in disease diagnoses
The officials claim improved sanitary conditions at water-treatment plants made cleaner water, which reduced disease incidence. This is a causal claim linking better water treatment directly to fewer disease cases.
To weaken this explanation, we need to find alternative reasons for the drop in diagnoses that don't involve water treatment improvements. We can attack the causal link by showing:
This choice actually supports rather than weakens the officials' explanation. If many new water-treatment plants have been built over the last five years, this would be consistent with the claim that improved sanitary conditions at water-treatment plants led to cleaner water and reduced disease incidence. More treatment plants would likely mean better water quality overall.
This choice is irrelevant to weakening the officials' explanation. The consumption patterns of bottled spring water by people with and without the disease doesn't affect whether improved water treatment at municipal plants caused the decrease in diagnoses. This information neither supports nor weakens the causal link between water treatment improvements and disease reduction.
This choice provides a strong alternative explanation for the decrease in diagnoses that has nothing to do with water quality improvements. If a new diagnostic technique is now correctly identifying many cases as intestinal ulcers instead of the intestinal disease in question, then the drop in diagnoses could be entirely due to better diagnostic accuracy rather than actual disease reduction. This directly undermines the officials' claim that cleaner water caused fewer disease cases.
This choice discusses the severity of cases among people who do contract the disease, but doesn't address the total number of people getting diagnosed with the disease in the first place. Whether people develop severe cases or not doesn't explain why fewer people are being diagnosed overall, so this doesn't weaken the officials' explanation about the cause of decreased diagnoses.
This choice actually strengthens rather than weakens the officials' explanation. If the water was brought up to high sanitary standards ten years ago and has presumably been maintained at that level, this would support the idea that good water treatment leads to lower disease incidence. It shows a longer track record of the relationship between water quality and disease prevention.