GMAT写作 逻辑错误之不充分采样错误

在上一次的GMAT写作中,说到了与数据相关的逻辑错误中的偏采样错误,今天我们继续来谈谈此类错误中的“不充分采样错误(The Insufficient Sample Fallacy)”。在argument中会引用一些来自某项涉及“样本”的研究、调查或民意测验的统计数据,接着就会得出与该样本代表的更大的集体或人口相关的结论。但是为了使某个统计样本能准确地反映一大群人的情况,该样本必须满足以下两条标准:
(1)  样本作为整体的一个部分必须具有足够大的数量(2)  样本在相关的特性方面必须具有整体的代表性
但实际上,argument中涉及到的样本采集往往缺乏足够大的数量或能代表一个整体,从而使得出的结论无法具有足够的说服力。
比如下题:
The following appeared in a newspaper storygiving advice about investments.
“As overall life expectancy continues to rise, the population of ourcountry is growing increasingly older. For example, over twenty percent of theresidents of one of our more populated regions are now at least 65 years old,and occupancy rates at resort hotels in that region declined significantlyduring the past six months. Because of these two related trends, a prudentinvestor would be well advised to sell interest in hotels and invest inhospitals and nursing homes instead.”
分析这段文章,可以看出作者得出结论“投资者应该卖掉所持有的酒店权益,转而投资医院和养老院“的基础是老龄人口的增加和酒店入住率的减少,并且举例说某地区20%以上的人口为65岁以上的老人,而该地区酒店的入住率在过去的6个月中明显下降。从“不充分采样”的观点得出作者在举例的时候并未明确说明“某地区”的具体信息,而“该地区“的情况是否能代表整个国家并不可知,也许某个地区恰好是老龄人口集中的地区,或许采样的这半年中也恰逢气候条件不适宜度假,从而得出的结论就不能适用于更大区域。在分析出逻辑谬误后可以采用以下方式(中心句/逻辑缺陷-驳斥/其他解释)展开论点:
The author provides no evidence to supportthe claim that the population as a whole is aging and that the hotel occupancyrate in general is declining. The example cited, while suggestive of thesetrends, is insufficient to warrant their truth because there is no reason tobelieve that data drawn from this unnamed region is representative of theentire country. For example, if the region from which the data was gathered wasFlorida, it would clearly be unrepresentative. The reason for this is obvious.Florida is populated by a disproportionate number of retired people over 65years old and is a very popular vacation destination during the winter months.Moreover, resort hotel occupancy in Florida typically declines significantlyduring the summer months.
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